Brown ploughs on, but for how much longer?

Prime Minister Gordon Brown was in the West Midlands today to discuss Labour's election manifesto with union leaders and members of Labour's policy forum. Business as usual? Anything but, writes John Hipwood.

The Scottish National Party's stunning victory in the Glasgow East by-election has increased the likelihood that Mr Brown might not even lead his party into the next general election. How the Scots love putting one over on the English. But hang on. This was the Scots putting one over on the Scots.

This was very nearly the Scottish Prime Minister's back yard, and let's not forget that his cabinet is liberally sprinkled with Scots who fill the jobs of Chancellor, International Development Secretary (and election organiser), Scottish Secretary (fair enough), and Defence Secretary (same person).

The SNP rejoices after their success. They are building very astutely on their victory in the Scottish parliamentary elections.

This was a vote not so much for the SNP but against the Labour Government in London. Mr Brown, in Warwick today giving a keynote speech to party members, will put his head down and plough on.

But he cannot now go on holiday to Suffolk next week nurturing the hope that things will settle down during August as the British people come to terms with the economic problems facing the nation. I In September he is expected to carry out a cabinet shuffle in time for the Labour conference in Manchester, which will now be dominated by the leader's future and whether he should be replaced before the next election.

In the present economic climate, few MPs believe that Labour can win the next election, but dumping Mr Brown would certainly do one thing - it would bring forward the election date. If he stays in No 10, Mr Brown will delay the election date as long as possible, probably until the spring of 2010.

But if Labour changes its leader twice within the same parliament, the new man or woman would have to promise an election within a month or two. It wouldn't be sustainable to change the prime minister twice without voters having a say in the matter.

A fresh face can work wonders as recent history showed when John Major won in 1992 . Could David Miliband, Ed Balls, Andy Burnham, James Purnell or Harriet Harman pull off the same trick for Labour?

You would have to say it's very unlikely, but there will be some MPs who think one of them might just do better than Mr Brown.

David Cameron today cleverly called for a general election in the autumn, but he won't get one. Mr Brown toyed with one last year, but there's no possibility of one now.

The Conservative leader won't mind too much. He's one person who will be quite happy to keep Mr Brown in Downing Street for a while longer because the Prime Minister is proving a nailed-on electoral liability.