The bill faces a stormy ride at Westminster

The government will publish details of the plans, to which 159 Labour MPs are opposed on Thursday.

Mr Blunkett, writing in the Sunday Times, warned ex-Cabinet members it was not the time for "grandstanding".

Newspaper reports suggest rebels may be offered concessions to get the Higher Education Bill through the Commons.

These could include writing off the debt after 25 years, bigger grants for poorer students or possibly a national bursary scheme.

This is not the moment for grandstanding in order to damage or embarrass the prime minister in pursuit of their own agenda David Blunkett Home Secretary

Mr Blunkett, a former education secretary, did not name the colleagues he had in mind.

But his message has been interpreted as being directed to allies of Chancellor Gordon Brown, such as Clare Short, Nick Brown and Frank Dobson.

The Higher Education Bill will allow universities from 2006 to charge variable tuition fees of up to �3,000 a year, repayable when graduates earn �15,000.

Mr Brown, the former Agriculture Secretary, told the BBC he would be prepared to oppose the government on the issue of variable fees.

He is among the Labour backbenchers and several former ministers who fear the fees may deter students from poorer backgrounds from going to the best institutions.

They claim the variable rate charged for different courses could cause a "two-tier" system.

Mr Brown told BBC One's Breakfast with Frost: "It is fundamentally wrong that access to the very best courses in this country should be by money and not by ability."

It is fundamentally wrong that access to the very best courses in this country should be by money and not by ability Nick Brown

Instead of a variable fee, Mr Brown suggested a compromise may be possible on the issue if all universities charged the same fee.

The motion opposing top-up fees has been signed by 159 Labour MPs, meaning Mr Blair could face a Commons defeat.

'Tough choices'

But Mr Blunkett has insisted the proposed scheme is fair and provides support for students from less well off backgrounds.

He wrote: "I find it odd that former Cabinet colleagues who had, with me, to make extraordinarily tough choices in our first parliament, find themselves unable to support us now as we respond in a similar way to new challenges.

Blunkett has rallied to support Blair

"This is not the moment for grandstanding in order to damage or embarrass the prime minister in pursuit of their own agenda.

He added: "I appeal to my parliamentary colleagues to take the trouble to look at the whole package, and recognise that it is fundamentally better - for poorer and middle income families alike - than the current system."

Currently, annual tuition fees of �1,125 have to be paid while studying.

Barry Sheerman, Labour chairman of the Commons education committee, told the BBC's World at One programme many opponents had now been won round.

But Norwich North MP Ian Gibson, who tabled the protest motion, dismissed the notion fees were needed to ensure middle class class graduates were not subsidised by the working class as a "red herring."

"If you look at the details of how much tax people pay, you would see that the so-called middle classes do pay a higher rate of tax for education than does the dustman," he said.

Earlier Conservative leader Michael Howard said he had "grave reservations" about tuition fees, but said he was reviewing his party's anti-fees policy.