It was late in the evening of 27 September 1981, and the tension in the Brighton conference hall was close to breaking point when the result was finally announced. After months of bitterness, the closest campaign in the Labour Party's history was over. "It's Benn - by an eyebrow," exclaimed the Daily Mirror the next morning. Tony Benn had unseated Denis Healey as deputy Labour leader.

Historians occasionally ask what might have happened if Healey had clung on. But with the union block vote in his pocket, Benn was almost unbeatable. The real miracle was that Healey came within 1 per cent of victory. Even so, Benn was on messianic form that night. "The forces of democracy and socialism cannot be stopped," he told his cheering supporters. "We are the masters now!"

In the weeks after the former chancellor's defeat, more than two dozen of his supporters jumped ship to the SDP, which was now well ahead in the polls. Healey refused to join them, instead retiring from parliament. In the meantime, Labour's travails went from bad to worse. Emboldened by victory, Benn moved in on the main prize just months later, denouncing his leader, Michael Foot, for supporting the Falklands campaign. And when Foot threw in the towel, "Brother Tony" took his place as the Labour leader for the Remembrance Day service at the Cenotaph in November 1982.

A year earlier, Foot had been derided for wearing a green coat described by some as a donkey jacket. But Benn in fact did appear beside Margaret Thatcher and David Steel in a genuine, black, woollen donkey jacket, complete with numerous badges: CND, "Right to work", "Ireland for the Irish" and a tiny Argentine flag. Six months later, his manifesto called for the abolition of the monarchy and the Lords, withdrawal from the EEC and the nationalisation of Britain's 25 biggest companies. Foot's sardonic verdict? "The longest suicide note in history."

Benn's political annihilation in 1983 marked the end of an era. With the Labour Party overtaken in the polls (although not quite in seats) by the SDP-Liberal Alliance, more MPs joined David Owen and Shirley Williams. Four years later, when the Alliance won its first general election, few people even noticed Labour staggering in a poor third. Certainly, Healey barely seemed to care: as Benn limped to defeat, he was playing piano for Lulu and Roger Moore on Dame Edna's Election Special. "It's always nice," he said later, "to have the last laugh."