The Conservative Party this week accused Tony Blair of having a secret agenda to raise the cap on top-up fees during the next Parliament.
The accusation follows revelations in The Times Higher a fortnight ago that key higher education figures had been prompted privately by officials from No 10 to campaign for the £3,000 cap to be removed despite a government commitment to maintain it until at least 2010.
The Conservatives said this flatly contradicted Labour's manifesto commitment not to raise fees by more than the annual rate of inflation.
Tim Collins, the Shadow Education Secretary, said: "Tony Blair has already betrayed students' trust by introducing top-up fees after a categorical denial during the 2001 election campaign."
He added: "He cannot be allowed to get away with it again."
At the launch of Labour's education manifesto on Monday, Ruth Kelly, the Education Secretary, denied that Labour intended to raise the cap.
Ministers had acted to bring order to chaotic university finances, she said.
Ministers had legislated for higher fees and bursaries in the last Parliament to ensure there was an "orderly system" of funding for higher education, she said.
"The cap will stand at £3,000 - allowing for annual inflation uprating - and that's in the manifesto," Ms Kelly said when questioned on whether policy might change if Labour were re-elected.
The launch was a carefully choreographed affair that featured Ms Kelly, Labour's campaign supremo Alan Milburn, and Ed Balls, formerly the Chancellor of the Exchequer's right-hand man.