Yesterday marked the counterpoint of Labour’s landslide euphoria of May 1997. The resignations of home secretary Jacqui Smith, along with other ministers and MPs, sealed the end of Gordon Brown’s hope to recover from the chaos of recent weeks. The prime minister’s authority, already dangerously low, was shot to pieces.

Almost everything about Gordon Brown underlines his unsuitability for his high office. We’re told that he persuaded Smith two months ago to delay her departure. Yet that delay has damaged his reputation as much as Smith’s.

You’d have expected a serious political thinker and son of the manse like Brown to have anticipated the public’s reaction to the long awaited publication of MPs’ expenses and planned a convincing response. Yet Brown has given every impression of being taken by surprise. Three weeks into the saga, the prime minister could only suggest a slow moving constitutional conference. (Shades of the old joke: do nothing, not even a royal commission.)

Brown has certainly been an unlucky leader. The credit crunch and MPs’ expenses scandal would have challenged a far more adept and persuasive prime minister. He inherited the running sore of the Iraq war from Tony Blair. But wait: he was Blair’s near equal, and could have stopped Britain’s participation in that disastrous operation had he wanted to. He has no alibi for what happened in the 10 years before he moved next door.

Above all, Brown shows the wisdom of the expression ‘be careful what you wish for’. He was convinced he had a  divine right to be Britain’s prime minister. He was crowned Labour’s leader – and PM – without a vote. That may be constitutionally correct, but it left the people resentful that Labour had foisted this deeply flawed leader on the country. As we debate a new politics, we should decide whether a general election should be called when a governing party changes leaders between elections.

Labour must ditch Brown now. It cannot allow another 12 months of lame duck government. It’s time to elect a new leader, and give him or her the chance to persuade Britain that Labour deserves another chance. My choice would be Alan Johnson, the popular cabinet minister who is surely the most authentic ‘self made man’ in British politics today. It would be good to see a former postman enter Britain’s most famous address. Let Johnson secure the top job, and declare his intention to hold a general election within three months, along with a comprehensive programme of constitutional reform. (Including the end of the PM’s ability to decide the timing of elections.) He may lose. But change is Labour’s only hope.