Darling promise over tax change

The move was being seen as a further concession to backbenchers threatening to rebel in Monday's crunch Commons vote on the Finance Bill, but sources close to the Chancellor insisted it was simply a "clarification" of his earlier pledge to tackle the issue in this autumn's Pre-Budget Report (PBR).

As Mr Darling began a series of meetings designed to win over potential rebels, it was announced that an influential committee of MPs would investigate the impact of scrapping the 10p rate on Britain's poorest households.

The cross-party Treasury Select Committee, chaired by senior Labour MP John McFall, intends to complete its inquiry and produce a report including recommendations for action before the Bill reaches the final stage of its passage through the Commons.

Some 39 Labour MPs have signed a rebel amendment tabled by former minister Frank Field which would delay the implementation of the tax change until measures were in place to compensate the estimated 5.3 million people who may lose out.

And many more on the party's backbenches have expressed concern over the impact of the change on low-income households, raising the very real prospect of a Government defeat if the issue is forced to a vote next Monday.

Downing Street said that ministers would be "working hard" over the coming days to persuade MPs of the merits of the change, which was announced in Mr Brown's final Budget as Chancellor last year and comes into effect this month.

And there were indications that the charm offensive, which began with a conciliatory address to the Parliamentary Labour Party by the Prime Minister earlier, may be having an effect.

Keighley MP Ann Cryer, said: "While I have signed Frank Field's amendment, I am very hopeful it won't be needed after the excellent meeting.

"I got the strong impression that the Prime Minister and Chancellor were really listening to the concerns raised by MPs."