Times ÖйúAƬ understands that, in a number of high-level conversations, institution heads have been told that the Treasury will have no choice but to find a way of clawing back money if too many universities set fees close to the cap.

It follows last week's letter to the Office for Fair Access, in which the government threatens to legislate to allow it to intervene if there is too much "clustering" near ?9,000.

The guidance to Offa on how it should judge access agreements, which institutions must have in place if they want to charge more than ?6,000 from 2012-13, also contains suggestions that "reserve powers" could be used to force universities to spend a minimum amount helping poor students.

Geoffrey Alderman, professor of politics and contemporary history at the University of Buckingham, said the letter represented a "very sinister" threat to autonomy and would almost certainly push some institutions towards privatisation.

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He added: "I would be a little wary of thinking this is just a bluff because we are dealing with a coalition government, one partner of which has particular views about tuition fees."

David Palfreyman, director of the Oxford Centre for ÖйúAƬ Policy Studies, said the threat of legislation to keep down fees raised the potential "paradox" of a liberally minded government trying to take more control while cutting funding.

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He said: "It is all driven, as I understand it, because they are now panicking as they have got very little in the way of levers to stop everybody jumping on the ?8,500 or ?9,000 bandwagon."

The more specific warnings over the consequences of charging higher fees are understood to have been relayed to vice-chancellors in the days leading up to the publication of the Offa letter on 10 February.

One source told THE that heads of research-intensive universities were being reminded of their reliance on science funding, while others at teaching-focused institutions were told their student number allocations could be threatened.

Roger Brown, professor of ÖйúAƬ policy at Liverpool Hope University, said ministers had to use "rhetoric and tough talk" in the Offa letter because of the "awful dilemma" they have over the cost of student-fee loans.

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"They still haven't solved the basic problem that their student support regime is just too expensive," he said.

Professor Brown said he was concerned that the government appeared to be targeting the post-92 universities by emphasising that institutions should be judged on retention rates.

"I was very struck that they clearly want to use retention as a weapon against the ex-polytechnics whereas these are the very institutions that are in the vanguard on widening participation," he said.

simon.baker@tsleducation.com.