Can Mr Cameron hang tough?

James Forsyth reviews the week in politics

When the head of state herself has declared, after a lifetime of study, that ‘the British constitution has always been puzzling and always will be’, one wonders what hope there is for the rest of us if we wake up on 7 May to a hung parliament. We have become used to going to bed in the wee hours of Friday morning knowing who the new Prime Minister is. But this time the only thing that might be certain is the uncertainty. The Cabinet Office guidelines for a hung parliament are thorough and detailed. But they will not help with the media frenzy that is likely to be unleashed from Friday onwards: the news helicopters hovering over Downing Street, the 24-hour rolling commentary.

Many Labour MPs are wondering who, precisely, will prise Gordon Brown out of Downing Street if he loses. One told me that Mr Brown would interpret any indecisive result as a rejection of the Conservatives — and set about trying to establish a ‘progressive coalition’ with the Liberal Democrats. Constitutionally, in the event of a hung parliament the incumbent Prime Minister has the first chance to try to form a government. But Nick Clegg has said he will not support Mr Brown if Labour has neither the most votes nor the most seats. It is not inconceivable that Mr Brown will try to stay put. But then, as one Labour MP warns, ‘there’ll be a Ceausescu moment’.

There is one other way that Labour could stay in power. Mr Brown could be replaced by another member of the Cabinet who will offer the Liberal Democrats what they want: a second election under PR. Such an outcome is being discussed by MPs of all parties — but it has several snags.