Tony Blair has been delivered a second shock this parliament by backbench rebels determined to flex their muscles.

In a surprisingly large revolt over government plans to abolish stuudent grants and impose tuition fees, 31 MPs defied their whips and voted against the government - another 15 or so abstained.

Labour managers had been confidently predicting the rebels - led by veteran left-wingers Tony Benn, Ken Livingstone and Dennis Canavan - would only muster around 15 supporters at best.

But the tactic of playing down the vote badly backfired, landing the Prime Minister with his second biggest revolt after 47 backbenchers opposed his plans earlier this year to cut benefits to single parents.

There was never any doubt that the issue had stirred up some serious opposition among a group of Labour MPs and, once again, more than the hard core of rebels decided to either stay at home or sit on their hands and simply not vote.

Proceedings delayed

The government also employed all the usual tricks to limit the size of the revolt. MPs were allowed to stay at home for constituency business, last-minute concessions to the tune of £143m were made and, undoubtedly, one or two waverers were leaned on by the whips.

They also tried to delay proceeding until late in the night in a bid to keep the vote off TV screens, which angered many MPs.

But the most embarrassing element was the way all the attempts to dismiss the rebellion by Labour's managers blew up in their faces and they will now launch an inquest into exactly how they could have been taken by surprise so easily.

The rebels had been warning them to expect a revolt of this size, but their claims were brushed aside by ministers and whips.

The first signs the government felt it might have more of a revolt on its hands came when Education Secretary David Blunkett offered concessions to older and poorer students as well as single parents.

And during the debate, he even called on an old Socialist slogan to characterise the government's proposals - "to those according to their needs from those according to their means".

Hard core

But the £143m package appeared to have no effect on the rebels and appeals to their socialist beliefs carried little weight.

Once again the rebellion was led by the hard core, usually Old Labour MPs who still call themselves socialists and who have little to lose from defying their leader. Tony Blair already knows who they are and pays them little mind.

Tony Benn, in a typically robust Commons speech, summed up the rebels feelings when he said: "You should tax the rich, not the educated. This idea when you have a degree you ought to pay more taxation than people who have more money and no degree is ludicrous."

Labour was paying the price for Chancellor Gordon Brown's determination to stick to the former Tory government's spending limits, he said.

His rallying call was taken up by Diane Abbott and Dennis Canavan, whose amendment to the Higher Education Bill calling for grants to stay for the worst-off, gave the rebels a focal point for their anger.

For Mr Livingstone, the latest revolt must have further damaged his chances of being selected as Labour's official candidate for the job of Lord Mayor of London. But for the rest they are mostly beyond punishment.

They know they are probably already on Mr Blair's "troublemakers" list and can expect no favours from him.