Tony Benn took out an old "smoking" sign and put it on top of a "non-smoking" sign. Rules don't apply to him

He is a pretty unlikely hero. A few thousand miles to the left of me politically, Tony Benn, who has just announced that he will not stand again for parliament, is a pacifist who is anti-Europe and anti-American. Yet he is up there, in my personal pantheon, along with Mother Teresa and Dag Hammarskjold. Why?

Partly, it's that history: the man who threw away his title to work for the people, the anarchist who questions conventions, the party rebel who threatens Tony Blair's easy sleep. There's also the charm: the voice, the pipe, the exquisite manners that treat a street cleaner with the same respect as (indeed rather more than) a prime minister. Above all, though, Benn makes me uncomfortable, as I suppose heroes are meant to do.

I first met him as a fellow panellist on Any Questions about seven years ago. He had wowed the audience, giving the Tory government a hard time, distancing himself from the Labour leadership, teasing Jonathan Dimbleby. The politicians taking part in the programme answered cautiously, calculating how best to please the audience without straying from the party line. Not Benn: he shot from the hip in response to every question.

During our trip back to London from Bristol, Benn expressed surprise that I, who had admitted an interest in William Temple and R H Tawney, was not attending the Christian Socialist Workers' Party AGM, which he was addressing. So that Saturday, at some ungodly hour, Benn came to pick me up in his battered Mini. He bought me my ticket - first class, "because I'm travelling with a lady" - and we boarded the train.

The train to Sheffield is the one that Benn takes to Chesterfield, and everyone from the passengers to the ticket collector greeted him like an old friend. We sat in a non-smoking carriage, but Benn opened his briefcase and took out an old BR sticker that read "smoking" and placed it smack on top of the "non-smoking" sign on the window pane. He held up his pipe: "No one minds, do they?" he asked of the carriage at large. A chorus of "Go ahead Tony" greeted him: rules simply don't apply to Benn.

I asked him about the influences in his life. His mother, a fierce Methodist and co-founder of the United Reformed Church, had been foremost, he said. In his childhood, she would kiss him goodnight, and whisper: "You'll see, darling, tomorrow will be another wonderful day" - thus simultaneously blessing the future and erasing any trouble in the past.

The Christian Socialist Workers' Party AGM was held in a shabby hall in the heart of Sheffield. Thirty scruffy people, twice that number of chairs, and a table heaped with home-made sandwiches half-filled the room. If he was disappointed by the turnout, Benn didn't show it. Ignoring the podium, he pulled up a chair to the front of the room, rolled up his sleeves, and began to speak. He told a story about how, when a train got stuck in its tracks, its passengers were forced into camaraderie: people shared food and drink, young helped old, men helped mothers and children. I can't remember the details, but Benn turned it into a stirring metaphor for Christian socialism. The audience loved it; so did I.

I listened to him roar his convictions and reiterate his commitment to social justice, trying to convince us that his vision of Utopia could be turned into the here and now. He was pink-cheeked and perspiring: he'd gone full out for the few listeners. I felt guilty: I, too, should work myself into a lather on behalf of others, and aim to put my ideals into practice. He made me feel small, petty and selfish.

For 50 years, he has made fellow politicians feel the same. In return, they have branded him a loony and blocked his advance. But he has become the conscience of those who know they have not lived by their ideals. Perhaps that's what heroes do best.