So when should a minister resign?

Politicians have always been reluctant to take the blame for failure. Jack O'Sullivan looks at some who made their excuses and left

Michael Howard's unwillingness even to consider resignation over the Whitemoor and Parkhurst jail breaks should come as no surprise. After all, James Prior hung on to his post as Secretary of State for Northern Ireland in 1983, when more than 30 IRA inmates escaped from the Maze prison. Some are still at large.

Many look back to a golden age, with ministers falling on their swords whenever the performance of their departments was found wanting. But that time never existed. Ministers generally stay in their jobs at least until the next reshuffle, almost regardless of how badly they have performed their tasks. Lord Carrington was the last to dispatch himself honourably when in 1982 he resigned as Foreign Secretary, along with his fellow ministers Humphrey Atkins and Richard Luce. They took responsibility for failing to anticipate the Argentine invasion of the Falkland Islands.

Prior to that, the last resignation for ministerial failure had been by Sir Thomas Dugdale, who left the Ministry of Agriculture in 1954 over the "Crichel Down" affair, a scandal concerning the Government's failure to return land to its rightful owners after the Second World War. Sir Thomas had had no personal involvement in the mistakes made by his officials, yet still stepped down. At the time, Sir Winston Churchill, the Prime Minister, reflecting general surprise at this noble act, saluted Sir Thomas's sense of honour as "chivalrous in a high degree".

Contrast his behaviour with Norman Lamont, the Chancellor of the Exchequer, who failed to resign in 1992, when Britain was forced ignominiously to leave the Exchange Rate Mechanism after a day of financial chaos. He survived until forced out in a reshuffle. Likewise, James Callaghan merely moved sideways to the position of Home Secretary in 1967, after devaluation made his position as Chancellor untenable.

Sexual or financial scandals, particularly in recent years, have been far more likely than administrative failure to destroy a ministerial career. Churchill's government of 1951-55 was free of such scandals, whereas they claimed four ministers under Edward Heath (1970-74). John Major has lost a record seven front-bench colleagues as a result of public controversies, including Jonathan Aitken, Neil Hamilton, Michael Mates, David Mellor, Tim Yeo and the Earl of Caithness.

Looking back over the period since the war, a great cultural divide between the Conservative and Labour parties becomes apparent. Not a single Labour minister has resigned since 1945 because of his or her sexual behaviour. This compares with numerous philandering Tories. And the only financial scandal to oust a Labour minister was the fall of John Belcher from the Board of Trade in 1948, for, as he said in his resignation letter, "the acceptance of gifts and hospitality from shady wheeler-dealers" in the whisky industry. In contrast there have been six post-war Tory resignations over financial scandals.

Labour politicians specialise in leaving office over points of principle. Nine parted from the Wilson/ Callaghan Labour government of 1974-79 on matters ranging from opposition to EC membership (Eric Heffer) and distaste for education cuts (Joan Lestor) to Reg Prentice's general disenchantment with his party. They followed a long Labour tradition, noisily exemplified by George Brown, the deputy Labour leader, who resigned in 1968 over "the way the Government is run".

Such principled resignations often but do not necessarily prove fatal to a politician's ambitions. Harold Wilson became Prime Minister in 1964, 13 years after resigning from Attlee's cabinet. Likewise, Michael Heseltine became deputy premier in 1995, nine years after storming out of Downing Street when he failed to win agreement that Westland helicopters should be rescued by a European consortium in preference to an American buyer.

The Thatcher government, perhaps because it had such a strong ideological flavour, was the only post-war Conservative administration to shed ministers over principle at a rate that compared with Labour governments. Thus, Ian Gow, Nigel Lawson and Sir Geoffrey Howe all left top jobs after falling out with Margaret Thatcher. But none returned to office. As Mr Howard has realised, the tried and tested way to get on in politics is never to say sorry and never to resign.