GORDON Brown's 10p tax band woes are set to escalate today as MPs return from their Easter break.

With the Prime Minister ruling out quick concessions to ease the impact of scrapping the rate on low earners, Labour rebels are steeling themselves for an explosive Commons showdown.

About 70 backbenchers and six ministerial aides have publicly voiced concern over the changes, which were announced in last year's Budget.

Foreign Secretary David Miliband issued a desperate plea for unity, warning that electoral defeat was certain if the party `argued among ourselves'.

But former welfare minister Frank Field, who has been spearheading the mutiny, dismissed government promises to help the hardest-hit at a later stage.

"The idea that somehow we'll do something undefined in the future to protect the poorest people in work, just is not on for most Labour backbenchers," he said. "This is a core belief for us and my guess is once we're back in the Commons the government will get a real feel of just how serious our intent is."

Thurrock MP Andrew Mackinlay said Mr Brown was like a `rabbit trapped in the headlights of a car' and the situation was causing `massive dismay, bewilderment and frustration' in Labour ranks.

The Tories, who have pledged opposition along with the Lib Dems, demanded Chancellor Alistair Darling `get off his backside' and reverse the tax reforms.

David Cameron said: "This was a pre-meditated attack on 5.3 million of the lowest paid people in our country, hammering them with an extra tax bill at a time when if they go shopping the grocery bill has gone up, if they fill up the car petrol and diesel has gone up."

Mr Darling yesterday said the government had an excellent record of helping low earners, having introduced tax credits and the minimum wage.

But he added: "What I cannot do is to rewind the Budget."

Mr Darling denied the government was in the middle of a `car crash' and said he believed colleagues would stop short of voting down its plans.

Treasury sources have indicated that any scheme to compensate people affected on low incomes could cost up to £8bn.