Too Frank for his own good

Mr Field's remarks are clearly unhelpful to the Prime Minister. But he may also have done the Government a favour, if he has given the impression that he is driven by personal opposition to Mr Brown as much as by concern about low-income people who will be hit by the abolition of the 10p tax band.

Lobby journalists were invited at short notice today to a briefing by Ed Balls, the Children's Secretary and Mr Brown's former spin doctor, ostensibly to hear about the Government's plans for education.

What ensued was a remarkable attack on a Labour MP by a Labour cabinet minister, as Mr Balls suggested Frank Field was unwilling to support any proposals put forward by the Government to try to meet his concerns about tax.

Asked if he thought Mr Field was on a mission to bring down the PM, Mr Balls said: "I'll leave you to draw your own conclusions from what was said."

Labour MPs are genuinely upset and concerned about the effects of the tax reforms. But they are far less likely to join any rebellion if they see it as part of an effort to undermine their leader and, perhaps, open the door to David Cameron and the Tories.

Mr Field, regarded as the leader of the tax rebellion, has provided an opportunity for the Government to portray it as precisely that.