In 1974, I was a young actor in an English repertory theatre. I made a remark at an Equity (actors' trade union) meeting at which the person who had convened the meeting (Jenny X) was being verbally attacked. I simply suggested that we ought to let her say what she had to say. What some of the company members knew and I didn't was that Jenny was not an Equity representative, but an ordinary Equity member and card-carrier for the old Socialist Labour League, soon to transform itself into the Workers Revolutionary Party. The Party wanted control of the entertainment industry unions because they operated the means of communication. I was blissfully unaware of this politico-historical sub-text.

A day later I received a phone call from an actor who wished to meet me. Let's call him John X. He was another Party member, but he didn't explain that; his tactic was to turn up at the theatre with a local teacher (another anonymous Party member) to contact someone who, from one sympathetic but entirely apolitical remark, had apparently been marked down for sounding out. Not once was the Party mentioned; John presented himself as a fellow actor speaking about Equity issues and particularly the idea of all the entertainment unions forming one huge, powerful trade union. That seemed a reasonable idea to me. There was manipulation and deception by omission in full, subtle swing, but I failed to notice. Part of me sensed I was being led into something but I ignored that tiny warning voice in my head. It would have meant disagreement, debate and the establishment of firm boundaries, and that had always been difficult for me. I have always had the desire to be accepted and liked in company, and this fatal flaw in my nature made me ripe for proselytisers.

Over a series of 'social' visits I was obliquely briefed along what I later learned to be Party lines. Part of the inculcation was to be invited to an All Trades Union Alliance meeting at the Roundhouse in London. John X drove us there. One other actor in our company came along, but he was simply grabbing a lift to London to see his kids. When the political ordure hit the fan he, sensibly, was nowhere to be seen. On the way I proposed that we were living in a stagnant society. John contradicted me, times were very exciting, which I suppose they were from his point of view. We ran out of petrol on the motorway, his attention distracted from the prosaic need for propulsion by the drug of social analysis.

The meeting was declamatory and defiant, and we were all addressed as comrades, brothers and sisters; but there didn't seem to be many actors there. I caused some excitement by leaving my Cregan bag in the foyer. It's brand name was similar enough to Creggan (one of the troublespots in Northern Ireland) to grind the rhetoric to a halt and cause a nervous request from the platform for the owner to claim it. These were days of bombs and shooting, of 'hang the terrorists' stickers in tube stations and on telephone poles, when to have an Irish accent in Britain was to invite random beatings. Once I got further into the stream of the Party I learned that policy was to support the goals of the IRA but not condone the violence. To me, that seemed illogical: the IRA and violence were one and the same thing; that was the IRA's point. You couldn't support one without the other. But the political position, I was to learn, had to be opposite the establishment on everything whilst keeping to the high moral ground. Reason, human nature and anti-social behaviour could be ignored if they contradicted the political end.

Back in my regional rep company, I received drop-in visits from the local teacher and his earnest girlfriend, usually over a pint, keeping the debate alive in me, and eventually it was suggested that I should hold a company meeting and force through a resolution on whatever issue was appropriate to the Party's assault on the reactionary Equity leadership.

In the 70s, resolutions were as de rigeur as mobile phones are now. I don't remember the details, but I received another visit from John X and the teacher, who briefed me on what needed to be done and said. The director of the company was worried. I kept assuring him that the meeting was not about anything subversive and the desires of the company would be reflected in the resolution. This, of course, was nonsense. Drip by drip, the party line had been fed into me until I was virtually a ventriloquist doll. What was important was what the Party wanted. Enough of the company would be uninterested to make the task easier. A lack of interest eases the progress of the fanatic and the fundamentalist. While the majority don't turn up, the fanatic fills the meetings with his own kind and can push through his agenda. I was reassured that only a few people in the meeting would have the political will to resist and we knew who they were.

I was very nervous before the meeting, but during it discovered a demagogic power I never knew I had. I also discovered the high that oratorical power can provide - I was, after all, an actor. One company member told me it was disturbing watching my Jekyll and Hyde transformation into a firebrand socialist forcing through a heavy, extreme-left resolution. Before that meeting I was a popular member of the company; after it, friends became guarded around me and my relationship with the director was finished. I had lied to him and was startled at his naivety in taking such a simple political device so indignantly.

I reported to John and gibbered about how nervous I had been and about the tremendous 'hit' I felt. I remember actually saying "God, you can imagine how Hitler and Mussolini got off on it." I could have added Lenin, Trotsky, Stalin. I was probably drunk. I don't remember, but I imagine I would have settled my sense of triumph with a few pints of creamy, northern, working-class bitter. The point was that I had crossed a Rubicon and announced myself as someone with hard-left convictions, even though many of these convictions were borrowed or plucked from the crossrow of socialist clichés.

In the 1974 election I campaigned in an industrial constituency for the WRP candidate and that was a turning point for me. Up until then it seemed absolutely axiomatic that I would join. I had consumed the Trotsky dialectic and its literature, sold the party newspaper in the rain, had an opinion on everything and a forceful, articulate way of expressing it; but alongside the thrill of it (and it was thrilling, I had, after all, found a purpose) was a profound doubt I could never define. In the election campaign I rattled working-class doors in a Labour stronghold in the North and pinned voters to their doorsteps. Most voters had never heard of us and I watched the horror mounting as I set our manifesto against the transparent revisionism of the Labour Party. One old dear said: "You're not a communist are you?" "Oh, no!" said I, truthfully. We hated the Communists. And the International Socialists (IS) and the International Marxist Group (IMG) and every other left-wing movement. The Left has always fought its bitterest battles against the other Left.

Occasionally, I found genuine interest in what I had to say and intelligent debate; one man concurred with absolutely everything I said but declined to vote for us as it would be a wasted vote. He was right. I remember a pair of old Polish identical twins, dressed in shiny black suit jackets, collarless shirts, grey flannels and tartan slippers, listening to everything and agreeing that the country needed a bit of what we offered, but unfortunately it was political pie-in-the-sky and they would vote Labour. Others were very hostile. I had several doors slammed in my face.

The candidate put me off. He was unemployed - no big deal, I was often unemployed myself - but beneath the dialectic I thought he was a loud, empty yob who knew what he loathed but not what he liked. By his side his campaign manager, a thin, middle-class woman with frightened hair and prime-time hysteria, interrupted our working lunches and exhorted us to get out on the streets and "make the difference" with the Calvinist implication that we, and not the message, were what was failing. We got a thousand votes.

When I had moved on to another theatre I took up the banner again, sitting in tiny meetings when my mates were out getting drunk or laid. I even developed an interest in political folk music, God help me. One night John X appeared and with another member, shut my dressing-room door, slapped the Party Constitution in front of me and told me to join. I declined. My excuses were the usual: not sure yet etc. What were my objections? I exercised my talent for evasive loquacity, but they could see through me. My reservations were subjected to the usual smooth, reassuring ripostes and what started as debate degenerated into an interrogation. The constitution was put away and John X said accusingly and prophetically that those who didn't join usually ended up against them. I asked where the party would stand with someone who disagreed with them on an important point of principle. We would discuss it, was his answer - but if after all the discussion there was still disagreement? "Then that person would be asked to leave." There was no leeway, no bend. It was not a broad church. I was saving them time.

But my connection was not severed. I was a 'fellow traveller'. Could be useful, perhaps one day will join.

The truth is that some of the analysis of the WRP seemed correct to me and my relationship with them stuttered on for a while. I hit a key terminal moment in a Midlands hospital exhorting nurses to strike and force the government to invest more heavily in the NHS. While the nurses agreed with the principle of increased funding, our exhortations for industrial action were dismissed as they would lead to deaths. I knew the Party response and mouthed it chorically with the Party member whom I accompanied - "Granted, but if you don't strike more people will die. By striking you will be saving lives in the future."

Lives were irrelevant. Striking was what was important. How had I arrived at such a shabby place? At what point had I given up thinking for myself and swallowed the party line as unquestionable?

I cleared out after that. It was difficult. At an Equity AGM I found myself pinned against a car by a semi-circle of party members giving me the third degree for absenting myself. I got away by executing a backwards roll over the roof of the car (I was young then) and legging it. I answered neither my phone nor my front door for weeks, checked out the street outside my flat whenever I came home or left. If I encountered party members at work, I went into a kind of paralysis. If I saw one in a pub, I slipped out. A very good friend of mine joined. I couldn't speak to him for years. Only now do we have a friendship again.

I have heard that John X became an alcoholic. I met him in a theatre bar in the late 80s and he didn't recognise me, only asked me to repeat my name as if it sounded some distant, muffled bell.

I also played the boyfriend of Jenny X in a TV series in the 80s, deep in the Thatcher years. She had no recollection of me either. I had not joined the Party, so I was as invisible as Trotsky in Stalin's family album. Within ten seconds of being introduced to her at the first rehearsal, she switched on a seamless line of propaganda which concluded with her asking if I had ever thought of joining the party. All delivered practically in one breath. No talk about the script, or the parts we were going to play, or if I thought the director was a wanker, no interest in drama, just the compulsion to recruit and convert. The job was only a means to the mission. Hers was, by any standards, an astonishingly revealing insight into the nature of the cause junkie. She was from a very substantial middle-class background. One day somebody used the phrase 'working class' in conversation about nothing in particular. It had a Pavlovian effect. She suddenly became Chekovian and rhapsodised about how she loved the working class, didn't we? No, we didn't. We were from it. We were not Guy Ritchie.

Out of interest and for old times' sake, I agreed to go to a 'union' meeting up in Sheffield. This was years after my involvement and I was curious. It also tripped my left-wing wire. In the intervening years I had contemplated joining the Socialist Workers Party, then the Labour Party and done neither. Now I loathe politics. The essential question is: does an economy exist to serve a society or does society exist only to service an economy? In the pre-Thatcher years the first position was abused, with its demands for jobs-for-life and subsidy for inefficiency. When Brecht's bitch on heat seized the keys of the Kingdom in her slavering jaws, the politics of obsession were born and the second position became enshrined, and still squats unquestioned at the Sacred Heart of New Labour's spirit of plutocracy. So the political reflex in me has always remained strong though the allure of Trotsky tarnished with the Seventies.

When I went to the meeting in Sheffield, some of the faces had changed but it was the same old redundant, self-gratifying rhetoric. It was a union meeting in the slimmest meaning of the term. The WRP ploy was to describe what really amounted to a WRP platform as a "meeting for all unions." I can remember at an actors' 'union' meeting watching well-known thesps sit open-jawed while a bus driver from Bristol harangued through some idiotic motion, and in Sheffield I saw similar shock on other union members who had been tricked into making the trip from various parts of the country to find themselves marooned in Trotskyist fantasy and whinging. But deceit was the only way they could fill their meetings and delude themselves they had some popular appeal. Once in, startled trade unionists were a captive audience and the rhetoric and the pressure wove its orchestrated effect.

It didn't take me long to stop listening to the speeches and start scrutinising the Art Deco interior of the Sheffield City Hall. I had worked at the local theatre many years before, and left the meeting at one point to take a walk round the town and recall some old memories. When I got back they were very 'concerned' about my disappearance and had sent out search parties to find me. At that moment these people and their puritan seriousness became ridiculous. In the coach home I was able to resist the predictable pressure to join with complete equanimity and humour. At that point Jenny X, who obviously thought she had been nurturing a convert, burst into a fit of exasperation and blurted: "I don't know what kind of life you can have! I look at my sister and all she does is have people to dinner." This moment of existential bewilderment spoke volumes and offered me an insight to which I could relate. It confirmed some awareness I had developed about how I had been sucked in and felt the sweet narcotic of zealotry.

We have to, as Marx advised, place everything in its historical context. 1974 was the beginning of the death of one-nation Conservatism. Edward Heath went to the polls, lost and was struck down by Thatcher, pregnant with the dogs of down-marketism, de-regulation and shopping malls where society had once stood. Prior to this golden dawn of philistinism and the canonisation of estate agents, we had to limp through another four plodding years of Jim Callaghan's old style Labourism, and watch the trade unions cruise the country looking for someone to kill them off.

However in the heady days of 1974, in a fug of Player's No 6 or Old Holborn roll-ups, such a future seemed unlikely. But anyone capable of a moment's reflection could have seen something apocalyptic coming. We couldn't continue subsidising our own incompetence. Ted Heath's Tories and Jim Callaghan's Labour party seem distant pieces of memorabilia alongside car jackets, buckled slip-on shoes and twin-tub washing machines. Some people may nostalgically yearn for those years of the closed shop and industrial unrest, when every Rover car that was exported lost the country £400 and trade union leaders stood up against the nationalised monoliths for the right to a job for life no matter how big the financial haemorrhage. The word 'principle' baulked heavily in vocabularies then, we all had them; it was much easier to cling to a principle than to think for oneself, and that, perhaps, was the psychological prestidigitation that provided access to a strong sense of being in the right. Now, of course, winning is all; being right is not market friendly. The Blair/Campbell axis has finally defeated principle, language and statistics. Statistics are a diversionary artillery barrage fired every time a difficult question is asked. Words can mean whatever the speaker wants them to mean, even if they contradict what he said five minutes before. The only imperative is to have the last word. If Jean Paul Sartre were to rewrite his classic play Huis Clos, in which Hell is two other people with whom you have to spend Eternity, Alaistair Darling would surely be one of them.

The world needs an intelligent new restraint to the gluttonous force of global capitalism. But today there are no obvious alternatives. In 1974, the disaffected could still turn to the off-the-peg Marxist variants.

Jung said "All forms of addiction are equally dangerous; whether they be to alcohol, morphine or idealism." Radical politics held seductive enticements for those of us with a floating sense of the world's injustice and who wandered life feeling not quite whole. I am not suggesting that radical politics recruits only from the ranks of the emotionally dysfunctional and the lost, but neither do they waste their time canvassing the mature and well-rounded. Nor do I dismiss radicals as cranks on a par with religious fundamentalists or New Ageists seeking the Answer; they are far too intelligent and have too much of a kind of integrity for that - the people I met in the WRP were decent, but once fired by the rhetoric, they transformed. It was like a kind of righteous alcoholism; Trotsky was a mood-altering substance. But when I wondered what it was that enmeshed me in radical politics for the brief period in the early Seventies, it became clear to me that the attractions were as much psychological as political. Laying aside perfectly rational objections to contemporary politics, what I found within the radical world was a community (friends), a language which structured my way of thinking about the world (understanding); an intellectual stimulus; an identifiable 'class' enemy: a sense of purpose and participation in something worthwhile (a sense of being useful). Above all, for a short but wonderful period, I experienced a feeling of being authentic.

It passed.

Considering the self-validation that a sense of being authentic endows, it becomes easy to understand how, if you add to the rationale a distorted history, a false sense of heroism, a gun and a mini-cab of Semtex, then you can go beyond the radical, straight to the righteous murderer for whom every shard of suffering, death and disablement is easily justified in terms of the future and the greater good. Had I been born in Belfast it might not have been the Trots who tripped my wire.