Tony Blair faces a humiliating defeat over his schools reforms this week with more than 100 Labour MPs preparing to register their opposition.
He has enraged his own backbenchers by co-operating with the Conservatives to force the Education Bill through its second Commons reading on Wednesday.
But David Cameron, the Tory leader, is planning to order his troops to vote with the Labour rebels on a second vote that will remove ministers' control over the legislation's next stage. He will claim that he is supporting the principle of the reforms but ensuring that the Bill is given the closest possible scrutiny.
Mr Blair could lose the so-called "programme motion" by such a crushing margin it would seriously undermine his authority, senior Labour MPs said. Gordon Brown, meanwhile, has been asked personally to call wavering backbenchers in an attempt to stave off the rebellion. But Mr Blair has been warned that a hard core of around 60 Labour MPs are ready to vote against the Bill on principle.
One senior Labour figure said: "This is more dangerous than losing the Bill itself. Blair can hardly occupy the high moral ground when he is co-operating with the Tories himself."Reuse content