He stayed longer than expected at Chequers, his weekend retreat, preparing for the knife-edge Commons vote tomorrow night and Wednesday's long-awaited report by Lord Hutton into the death of Dr David Kelly.

Despite a dramatic plea to the rebels from Gordon Brown yesterday, Mr Blair knows there are still enough Labour MPs ready to "betray" him in the fees showdown despite a last-ditch change to the Higher Education Bill yesterday.

Charles Clarke, the Education Secretary, pledged to write into his Higher Education Bill a guarantee that the 3,000 cap on annual fees would not rise for the whole of the next parliament.

Mr Clarke also hinted strongly at more help for medical students after an outcry over the levels of debt that newly-qualified doctors could face under the proposals.

Mr Brown weighed in with a direct appeal to rebels to back the "important and radical reform...that is necessary for both opportunity and for excellence in our universities".

He told GMTV: "I believe that we will win. I believe it is right that Tony Blair and the Government do win this and I believe that it is a sensible, radical reform."

But even the Chancellor seemed to add to Mr Blair's discomfort by saying that it was a matter for him whether he stayed on as Prime Minister.

Asked whether Mr Blair would still be Prime Minister at the next election, Mr Brown said: "Should he be? Yes. Will Tony Blair be? That's a matter for him, Tony Blair has been a great Prime Minister for Britain and I think he has been a great leader of the Labour Party as well."

One organiser of the revolt said: "We are standing firm on our core concerns about the variability of top-up fees."

Dai Havard, Labour MP for Merthyr Tydfil and Rhymney, said that the plans were wonky and the Bill should be withdrawn.

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