At the end of July, 2000, a very assorted bunch of people with ages ranging from 20 to nearer 60, mostly Brits but with a Dane and a Malaysian, set off as 'Oxygen 2000' to climb a previously-unscaled Himalayan 6,000-er, to research how we perform at altitude and to see whether a particular vitamin supplement aided physical activity and prevented altitude sickness.

Returning to Delhi after 27 years, I found little fundamental change. There was a good deal more motorised traffic, but that is so everywhere. There were still beggars; some so piteously deformed that you wonder how they could continue with any sort of life, some obviously destitute, and others who simply expect to find rich foreigners a soft touch. Perhaps the overcast monsoon sky made it seem dirtier than before, perhaps memory was up to its usual rose-tinting tricks, but I think it really has become grubbier and has begun falling down around the ears of its citizens. There are piles of rubble everywhere. Not building or demolition sites, just rubble.

One is still beset by people who want to give a head or foot massage or to sell whatever. The asking price is usually at least three times what will be accepted; one man was so keen to sell me a chess set I didn't want that he offered to let me have it for less than a quarter of what he had originally asked... Auto-rickshaw drivers routinely ask for up to twice the quoted fare when they get you to your destination, having tried to browbeat you into visiting emporia along the way. They don't have change, so until you wise up and carry lots of small notes, you pay over the odds anyway.

Who can blame them - the poorest Briton is well-off compared with the lower tiers of Indian society, and the poorest Britons don't buy air tickets to Delhi. There are potentially more costly scams - the 'M33 scam' is quite elaborate. People met 'accidentally' confirm to a helpful bystander's story that the office where foreign visitors can buy train tickets from a tourist quota at New Delhi railway station is shut. If you go to the booking agent at M33 Connaught Place, however, he can to get you a seat. He will probably tell you that only first-class is still available, thus increasing his commission, and will charge a (by local standards) large booking fee. Because of the skill and the sheer number of participants, this scam almost worked on me. The fact that I decided to think about it because I didn't have enough money on me and some tiny alarm bell sent me back to the station to double-check whether the tourist ticket office really was shut for Lord Krishna's birthday saved me from paying more than twice what I should have paid for my journey to Agra to see the Taj Mahal. It would, of course, still have been worth it. I didn't intend this to be 'tips for travellers', even less a diatribe on the ways that can be found to part us from our hard-earned cash. I'll leave Delhi and head for the hills.

The hills in question are the Pir Panjal and Himalaya, but on the way we stopped in the old Raj hill station of Shimla. When the (British) government of India used to move there in its entirety to avoid the oppressive summer heat, the public buildings, built in English country town style, would have been more spic and span, but there is still a faded colonial charm, at least for the nostalgic English visitor. Before the narrow-gauge railway - the 'Toy Train' - was built, the journey must have been quite an undertaking. Sahibs and memsahibs in their carriages or on horsebac, armies of minions toiling behind with the oxcarts that brought up all that was needed to administer the sub-continent. The resident monkeys must have wrought at least as much havoc then as they sometimes do now. A local businessman had his bag snatched by one which proceeded to distribute large amounts of money from the rooftops. The British colonial police are said to have set up a department for simian crime.

Despite the seasonal rain, I should like to have spent a little longer looking around Shimla, but those hills still had to be reached. We had a permit to climb from the Indian Mountaineering Federation. Members of our expedition had spent hours poring over maps, satellite pictures and the few available photographs to identify a previously unclimbed 6,250m peak in the area near the Tibetan border which had, until quite recently, been closed to foreigners. During the early stages of the ascent we were to be guinea pigs in tests of the body's performance at altitude, so we were all taking piles of large pills which might, unless they were the placebo, help us to acclimatise better. The sooner we got on to the climb, the sooner we'd be able to stop swallowing them.

When a landslide (common on roads in the southern Himalayas at monsoon time) held us up, annoyance at the delay was tempered by relief at a respite from the tension of constantly overtaking in heavy rain on blind bends at the edge of enormous drops to the accompaniment of all possible permutations of the four notes available to our bus driver on his horn. At one stage the suppressed hysteria could only be overcome by everyone dancing in the aisle of the bus to old Western pop and a Bengali version of house music.

Ten hours or so of this interesting bus ride finally brought us to the hill resort and Indian honeymoon destination of Manali in the Kullu valley of Himachal Pradesh, to beers and welcome beds. The following morning in bright sunshine some of us rented an assortment of motorbikes and scooters to ride the 56k up to the 3,800m Rohtang La (La = pass) to walk about and begin adjusting to altitude. I had not ridden a motorbike before; since no one asked to see my driving licence, that didn't seem to matter. The road surface and hairpin bends stop you from going very fast, even downhill, and you tend to concentrate on avoiding potholes so much that you only notice the drop when you have to stop on the edge of it to let through some truck or bus coming in the opposite direction. At such times it is wise to hold your breath; if the other vehicle - usually a diesel - changes gear or decides a few extra revs are needed, you get a faceful of filthy black smoke. (For the benefit of US readers, this road makes the Going to the Sun road in Glacier Park seem like a major highway, and this one has no side wall!) On the way up you could see an eagle or more likely a huge Lammergeyer vulture sweep across your line of vision and you might see a yak as well as the assorted cows, sheep and goats that are common there. Around a bend, the chai stalls and prayer flags that mark the high point of the pass suddenly appear out of the mist. A bunch of nutty westerners on motorbikes seems to amuse the Indian tourists, most of whom have come up in jeeps or buses. After posing for photographs, walking around the litter-strewn area and having cardamom tea, we set off back down. Almost immediately the rear suspension strut on my bike parted company with its bottom fixing. I was just resigning myself to the prospect of a very long walk pushing a dead machine when my companions twigged I was missing and came back. With a combination of know-how and bootlace, a temporary repair was rigged. So temporary that it needed fixing again before long. But after a couple of adjustments it seemed strong enough to hold for the rest of the way down.

About 10k from Manali the afternoon rains began. Within a minute or so we were soaked to the skin, so off came the sunglasses that had been so essential on the way up and on went the journey.

After a shower and hot drink it was time to pack for the next stage of the trip - the move to where the walk in would start. Next morning we loaded everything and everyone including cooks, porters, tents, and a canister of liquid nitrogen (did I mention that our sadistic researcher planned to take blood samples along the way?) aboard a bus and set off over the Rohtang La again. About 20 minutes into the journey, a rear suspension shackle broke, but after an hour or so with the help of a local blacksmith we got going again. This time we went down the other side of the pass a way and then turned up the Chandra Valley towards Spitti.

If you look at the map you will see circles along that road labelled with names like Chhatru, Chota Dal and Batal. You might expect these to be villages. Not so. Each has one or two buildings, one of which is a dhaba - an extremely basic café formed by throwing a large tarpaulin over a set of dry stone walls. Around these, most vehicles stop for the night and their occupants either pitch tents or sleep in the cab.

Leaving the first dhaba in the morning to walk to the next (part of our acclimatisation programme), we were followed by a dog. We determinedly ignored it, but it trailed about 20 metres behind us. At the end of the day it was still there, still completely ignored, quite healthy though slightly cowed. We assumed it would eventually wander off home. Next morning it was still around and we threw it some stale bread. That might have been a mistake. It was with us throughout the next day too, plucking up courage to follow a little closer behind as we went over or around the big landslides and rockfalls that blocked the main route into Spitti. Some poor souls had been stuck with their vehicles between falls for several days, and there was a steady file of people carrying their luggage across, hoping to find onward transport on the other side. We stopped for lunch at a pleasant spot above one of the places where the road had been washed away by the monsoon, which was striking much further north than usual in areas normally reckoned to be in a rainshadow. A man stood up on a rock a short distance away, gesticulating and blowing a whistle. We soon realised that he was not a lunatic. He was about to dynamite the hillside. The point was to blast enough rock to fill the great gap, then roll it level-ish so that it could be driven over. We moved further up the slope and waited. Following a loud bang, stones rained down on our picnic spot and even whistled past our new position. With no further problems (apart from a mudslide coming between our front runners and the main group), we pressed on to Batal for tea and biscuits in the dhaba while we waited for the horses to arrive with our tents.

Tea has improved since my last visit to India. Tea, milk and sugar are still put in a kettle together, but the longlife milk now used makes the brew less sickly than when condensed milk was the norm. Even now, though, such tea (or 'chai') is often rather sweet; black tea - or black tea with ginger - is sometimes a better option, as one can usually sugar it to taste.

Batal was our last taste of anything approaching mod cons for some time. The next day we left the road and set off up the old trade route via Chandra Tal (Tal = lake) towards the north. Packhorse trains still make their way up the valley to where three such routes meet at the Baralacha La, but now they almost all carry tents and kit for trekking parties. Fortunately, there are not so many that the sense of space and emptiness is lost, but one is rarely completely alone. In Summer you can usually see, in the distance or on an apparently inaccessible steep mountainside, a yellow (or, more often, a blue) speck, the plastic sheeting that herdsmen now use to roof the dry stone walls of hut circles (or rectangles) that were probably built by their forefathers generations ago. Talking to one such man who was looking after goats and a mass of frisky kids by his hut, I discovered that he had set off on foot nearly four months earlier in April from his home near Manali, which we had left by bus. He was about to start the return journey with his flock - going from hut to hut and from patch to patch of sparse grazing - and expected to get home some time in September. All the time he was in the wilds, he would live only on what his horse carried and what his animals provided. He cooked over fires of dried dung, since there is almost no wood or even scrub around; drew water from springs and streams; took milk and occasionally meat from his sheep and goats to supplement the flour and rice he had brought with him; and smoked tobacco in his hubble-bubble. I hope he was not offended that we declined to share a smoke with him. Our brief conversation reinforced my admiration for the hardiness of hill peoples everywhere. The wandering herdsmen of the Himalaya must be among the toughest of them.

We did not talk of the majestic, starkness of the mountains around us, and I wondered whether the familiarity of his long annual visits might have made him immune to their beauty. A few hours after meeting, him the browns and ochres of the enormous scree slopes and crags were interrupted by another blue speck. This time, though, it was more turquoise and rather bigger. Chandra Tal is not a huge lake - it's about a kilometre long. Though it is at an altitude of over 4,200 metres and is fed by meltwater from the snows and glaciers higher up, it is not very deep and therefore not always very cold. The temperature is more English south coast than Mediterranean, but in the late morning and early afternoon sun, before the wind gets up, it provides a very refreshing dip. The notion that you are swimming at an altitude higher than most European mountaintops is quite exhilarating.

Camping by the lake was a Breton family, who seemed pleased to chat and exchange stories. Irene, the mother, was waiting for her husband to come back from checking the river crossings further up the valley - parties coming down had told of rivers much too full to cross, which was bad news. The rivers swelled each day as the sun melted snows higher up, but the abnormal rains had made them more dangerous than usual. When her husband returned, his news was not very promising. We decided to press on anyway: they would make their decision as late as possible in case conditions changed.

After a bracing 6.30am swim in the lake, we set off over some quite rough ground cut across in places by the steep V's of meltwater streams. Their thickly-mudded sides were vivid evidence of just how deep such streams can become when conditions turn nasty, but those we crossed were low enough to manage without much difficulty and narrow enough to do so without getting too wet. When we stopped for lunch, the temperature was 42 degrees C in the sun and there was no shade except our brollies. This was one of the longest days of the walk-in and as we tiredly got our tents up, the afternoon rain began to fall quite heavily. Suffering from a sore throat, and rather cheesed off with sitting hunched up and damp in the overcrowded mess tent, I crawled gratefully into my sleeping bag for an early night.

A somewhat fevered night saw me awake and up before six to be greeted by the sight of fresh snow on all the nearby tops. Beautiful, but not really what you want when you are planning to go up. We were not planning an ascent that day, however; we still had to reach our mountain. We also had to make our blood sacrifice. In the name of scientific research (and of Phil's PhD), we not only had to have samples taken but also had to set up a centrifuge to separate them. Because blood thickens with altitude, just getting a syringe full from some of the team was difficult; with nothing resembling a table to clamp it to, setting up and operating a hand-turned centrifuge was even more of a problem. A flattish rock and even the jawbone of an ass held in place by a few rocks were tried before the eventual solution was reached. An ice-axe was set between two large stones with two more large flat stones on top. On each of those someone sat. That gave just enough rigidity for a third person to turn the handle for the required quarter of an hour or so. Then the separated samples were labelled and put into the tub of liquid nitrogen which had come all the way from England, doing the last stretch of the journey on the back of a donkey. It was apparently a first for science. Blood samples had been collected at higher altitudes before but not spun to separate the plasma and the corpuscles. Wow! The other part of the scientific ritual involved measuring things such as body fat and pain threshold. This was called a rest day. I was glad of it, as my throat was still sore. We washed ourselves and some clothes.

Next morning the trekkers decided they had little chance of crossing the river immediately in front of us (and the one further up the valley was reputedly worse), so they set off back down to find other adventures. We set off up our side valley. After less than an hour, the leader of our packhorse drivers said that the ground was too difficult for laden horses. We would have to stop. He announced this in a small bowl with not enough flat land for one small tent, let alone our whole encampment. We thought it was a ploy to get more money from us and that we would be able to negotiate - perhaps half-laden animals could do two journeys. As we went ahead to reconnoitre, they were unloading kit. They were not trying to get more money from us. They had decided that there was a killing to made by going back to the roadhead and ferrying travellers' and traders' loads around the landslides when lorries had to stop. They couldn't finish their job with us - they had to get back down before the landslides were cleared away. Some of our party went to announce they had found easier ground only to see the rear end of the last of the horses disappearing down the mountainside...

So we were now in sight of our mountain, only a day or two away travelling at our previous pace, but with a mountain of gear and no transport. It would not be possible for us to ferry everything that far on our own backs in less than four or five days. We would have to allow the same again to get back to meet the next team of mules and horses that was to get everything back to the road after the climb. That did not leave us enough time to recce and climb the mountain.

It was galling to be in sight of what looked, through binoculars, to be a challenging but manageable peak and to have to give up. After a brief conference, we decided to have a go at the nearest reasonably high mountain. I didn't take much part in the discussion - I was too busy coughing and spluttering. Breathing at 4,600m can be effort enough without a chest infection. The others kindly told me not to bother joining the portering party who were lugging all the stuff from where the horse team had dumped it up to the small flatter area which was to become base camp. I busied myself cutting tent platforms and took to my sleeping bag at the earliest opportunity, hoping this did not mean the end of my chances of getting up anything at all.

The others organised and set up an advanced base camp across the river and a bit higher up. One woman lost her footing and was bowled over by the force of water, knocking her leg on boulder in the process. Numbed by the cold water, she didn't realise at the time what a bash her leg had taken. The better weather which, ironically, had started as soon as the horses deserted us had probably melted all that fresh snow of the past few days and made the river more of a barrier than it should have been. Wendy was one of the last to cross and had quite likely left it too late in the day.

I watched through binoculars the next day as tiny figures, some recognisable from the colour of their clothing, made what seemed to be painfully slow progress up the steep scree that made up much of the mountain, much of the whole landscape thereabouts. What I couldn't see was that Mutley had also set off with the first group of climbers and eventually slept out at over 5,000m when they bivvied for the night.

I was beginning to get over the bug that had floored me and thought I'd be ready to cross the river next morning - too bloody late, I thought, everyone will already have climbed it.

Thinking that even if I couldn't get up the mountain because everyone else would already have climbed it and would be unlikely to want to go a second time, I decided to cross the river next morning anyway. If nothing else, I could go up to Advance Base Camp and lend a hand with lugging things back over. I set off after another hearty breakfast provided by Bruce Lee (lookalike), our camp cook who had been looking after me and feeding me up while the rest had been living off ration packs. When I reached the river at about 8.30, I found myself being directed towards the best place to cross by Phil, who had come down from the other side for a wash. Although fast, the water was then only a little above knee deep, so I took off my socks and inner boots, rolled up my trousers and - leaning on my trekking pole - waded over to join him. It was like fording a river of ice cubes. I was grateful to sit and dry my feet in the sun before setting off up the steep slope on the far side to the camp. I learned that Phil and Craig (at 20, the youngest of the group) had gone off well before the main party but had taken a wrong line and had to come back down to ABC because they could not find water on their route and needed to get more food before going again. I would be able to try it after all, though it might prove to be pretty demanding to keep up with those two (the older was little more than half my age, and the last thing I wanted to do was to slow them down), but we'd give it a go.

In the afternoon, partly to break the tedium of sitting about camp, I wandered a couple of hundred metres further up to watch for the returning climbers. They had set off relatively late on the previous day and had made differing rates of progress. Martin, a strong and dogged soul, had slept out at about 5,200m and the rest a few hundred lower. Getting up and away at different speeds in the morning after a night of little sleep, separated them further and Alec, who had done so much of the research involved in setting up the trip, had to give up because of altitude sickness. This was miserably ironic as he had helped to devise the acclimatisation programme that spared most of us the same problem.

The rest had all made it to the top. Fortunately for Martin, ropes were not necessary. Otherwise he would have to hang about waiting for someone else. On the snowfield it was possible to avoid the steepest, iciest section by a ramp to the side. Then it was straightforward, though still pretty arduous because of the thin air, all the way to the summit ridge.

We learned all this from the main party as, in ones and twos, they staggered back to ABC. For most it was the highest they had ever been. The maps we had of the area did not agree on the height, and our altimeters gave a different version again but it was clear that the mountain was not much short of 6,000m.

Leaving the exhausted summiteers of the previous day to sleep off their two days on the hill, we set off before seven next morning. All three of us were feeling pretty good and we made very good time reaching the lower bivvi site in a good bit less than half the time the others had taken. We continued to make such good time that when reached Martin's higher bivvi site, we decided to stash some of our gear in the rocks and make a lightweight dash for the top. There was plenty of the day left. At worst, we would have to sleep out when we got back down to that point: at best, we'd make it all the way down.

We munched some calories, had a drink, a short rest and an aspirin to ward off the slight headache we were all beginning to feel and set off again. We must have been exhilarated with how well we had been going because we still continued to steam up the slopes. I was just about managing to keep up with the other two (I don't think they were being kind in the pace that was set). Even on the ridge leading up to the summit we managed a fairly consistent 25 paces before pausing for breath - better than I'd ever done before. I was certainly thankful to Alec and Graham, the team leader, for the acclimatisation walk-in they had planned.

The summit itself was a ridge of steep snow with a rock outcrop at either end. The views, which had been good all the way up, were staggering. The peaks we could see off to the east were in Tibet, those to the north in Ladakh, and those to the northwest in Pakistan. The Indian ones back the way we had come were pretty impressive too. Despite the elation, the wind made it too cold to stay long. After handshakes and summit photographs we headed back down, determined to make it back to Advance Base Camp that day. We descended what had been a two hours ascent in 20 minutes, collected the gear we had shed on the way up and pressed on. Although Craig's youth got him back about a quarter of an hour ahead of me, I was still extremely pleased to have completed the whole round trip in nine and a half hours - especially as only the day before I had thought I wouldn't be going up at all. It was not a classic mountain, but to ascend and descend about 1,300 metres, starting at not much lower than the height of Mont Blanc is quite a lot for a day trip.

We hadn't reached the unclimbed peak we'd planned to climb when we left England and that we had seen looking much more challenging in the distance, but it had still been enjoyable and satisfying in the masochistic way that mountains and, so I'm told, running marathons can be. And we still had to get back to the 'corner', the river confluence, where the next packhorse team was to pick us up.

There were still some adventures in store - saving a party of stranded French people from a freezing night on the other side of the river, the killing of the (not very) fatted ewe, and the horseman who managed to lose his horses - but the mountain tale is told.