The prime minister was forced yesterday to deny that he might quit Downing Street before the general election after suffering a double-barrelled blasting by Charles Clarke.

The prime minister was forced yesterday to deny that he might quit Downing Street before the general election after suffering a double-barrelled blasting by Charles Clarke.

He also dismissed questions, on American TV, about whether he is slowing going blind. He lost the sight in one eye in a teenage rugby injury, but he emphasised in an NBC Nightly News interview that the vision in the other one 'is not at all deteriorating'.

Mr Clarke warned that Labour is heading for a general election 'hammering', and that it might not even have a future afterwards as a major political force. The Norwich MP and former home secretary also intimated that Mr Brown should stand down - possibly blaming poor health - to protect his dignity.

'I don't think Gordon will lead Labour into the next election. I think his own dignity ought to look to that kind of solution', he said in an interview with the London Evening Standard.

Rumours had already been circulating at Westminster that Mr Brown might stand down 'on health grounds' to try to save his party from an election catastrophe. But when Mr Clarke's comments were put to him - in New York where he was attending UN meetings - the PM stressed that he is fit and resolved to lead his party into the election.

'I'm healthy and very fit. I run a lot to keep fit. I keep going, and I've got a job to do', he said.

He suffered a further blow at Westminster when a Labour MP resigned as a parliamentary aide to the government's law ministers over the fact that the attorney general, Baroness Scotland, has not resigned or been sacked despite being fined �5000 for employing an illegal immigrant. Stephen Hesford protested that she should have resigned.

Mr Clarke told the Standard that on current form, Labour will 'get hammered' in a 2010 general election. And later in a speech to the Blairite pressure group Progress, he said that the government's level of performance 'is likely to lead to the loss of well over 100 Labour seats' and possibly 150.

The election would determine the shape of British politics for the next generation, he added. That included the place of the trade unions and the Labour Party within it - 'if indeed they have a future after the very serious defeat which opinion polls currently predict'.

Mr Clarke told Mr Brown to his face that he should quit at a meeting of the Parliamentary Labour Party in June. He did not explicitly repeat that call in his comments yesterday - delivered at a highly sensitive time just before the start of the Labour conference - but the theme ran clearly between the lines of much of what he had to say.

The Norwich South MP also expressed mounting frustration with colleagues who are privately in despair about their party's prospects under Mr Brown but are keeping their heads below the parapet.

'Are we just going to stand by and watch the whole Labour ship crash on to the rocks of May 2010 and sink for a very long time? Or are we going to try and do what we can to stop that happening?' he asked.

He voiced particular exasperation with 'New Labour' colleagues who 'believe that there's no hope for 2010' and that 'there's nothing to be done but knuckle down behind the current leadership'.

Mr Brown is not expected to run into strong opposition at the Brighton conference. But there is a possibility that the mood will shift decisively against him among Labour MPs when the Commons returns on October 12.

Mr Clarke argued that there is still a route to a Labour election victory next year. But he made it clear that it will not be found, in his opinion, under the leadership of Mr Brown.

'The Downing Street operation is the weakest I've seen ever in my life', he said. 'Our leadership is weak, uncertain, tactically unsure and lacks vision. We are unpopular. And, worse than unpopularity, all the evidence is that Labour is not trusted.'

It was possible, he conceded, that economic recovery and a Tory implosion could deliver Mr Brown an election victory. But this was not a view 'most people in Labour, including myself, share. And it would require the heroic improvement in our political performance which continually fails to materialise.'