Backbenchers' mutiny in 10p tax row

The scale of support for former minister Frank Field's amendment puts Mr Brown's 67-strong Commons majority on a knife-edge, and will mean ferocious lobbying over the coming days by ministers and whips determined to limit the size of any revolt next Monday.

One Labour backbencher questioned whether the Government could survive defeat on such a key Budget measure, and called on Mr Brown to make clear by the end of next week how those losing out from the abolition of the 10p band would be compensated.

But an ICM poll for The Guardian had better news for the Prime Minister, cutting the Conservatives' lead over Labour from 13 points last month to just five now. Among those questioned, some 34% supported Mr Brown's party (up five), 39% David Cameron's Tories (down three) and 19% the Liberal Democrats (down two).

Mr Brown was in conciliatory mood when he spoke to the Parliamentary Labour Party about the tax changes, promising he had listened to their concerns over the impact on the poorest workers and would "sort out" the problem by the autumn.

The Treasury announced that a review of measures to tackle child poverty would be extended to include low-income households without children, who are thought most likely to lose out from the change.

Chancellor Alistair Darling is expected to announce the result in his Pre-Budget Report this autumn, with speculation revolving around possible increases in tax thresholds or extension of credits to offset the loss of the 10p band.

But this was not good enough for some Labour rebels, including former minister Mr Field, who tabled his amendment immediately after the Finance Bill, which implements Budget decisions, cleared its second reading in the Commons.

His office said that the amendment, which would delay the removal of the 10p rate until measures to compensate losers are in place, carried the signatures of at least 35 Labour backbenchers and possibly as many as 40.

It is estimated that as many as 5.3 million households - many of them low-income workers without children - will lose around £3-£4 a week as a result of the change, announced by Mr Brown in his final budget as Chancellor last year and which is coming into effect this month.