Tens of thousands of soldiers, sailors and airmen on the lowest armed forces pay bands will be between £30 and £89 worse off from this week as a result of the abolition of the 10p income tax rate, according to Liberal Democrat research.

IAN BRUCE and ROBBIE DINWOODIE

TENS of thousands of soldiers, sailors and airmen on the lowest armed forces pay bands will be between £30 and £89 worse off from this week as a result of the abolition of the 10p income tax rate, according to Liberal Democrat research.

The revelation heaped further pressure on the Prime Minister after he had already faced one of his worst ever back-bench revolts over a tax change seen as an assault on the lowest paid. Members of the armed forces of private rank up to level 3, who have a starting salary of just £14,349, will be hit hardest. Those on level 1 are new entrants and trade apprentices.

In total, about 66,000 servicemen and women - up to a third of all armed forces personnel - could find themselves paying more as a result of Gordon Brown's tax changes.

Vince Cable, the LibDem Shadow Chancellor, said: "This is a shabby deal from ministers who appear to care little about those who put their lives on the line for Britain.

"How can we be asking our hard-pressed personnel to pay more in tax when we pay them so little in the first place? This is a disgraceful way to reward our armed forces for the fighting they are doing in Afghanistan and Iraq at this government's behest.

"Once again Brown and Darling have shown that what they give with one hand they take away with the other."

According to the Ministry of Defence: "The increases provided for by the pay review body this year included not only a 2.6% basic rise, but the addition of the X factor to increase the remuneration of the lower ranks by about 3.5%.

"That is on top of the 9% for the lower ranks provided for last year. The operational bonus also increased by 3.6%. In addition, retention packages of up to £15,000 for certain pinch-point trades are continuing to try to maintain skills in those areas where they are most needed."

The MoD last year introduced a tax-free operational allowance of £2320 for a six- month tour in Iraq, Afghan-istan and the Balkans. There is also an £1100 longer separation allowance for married troops. This amount is pitched to ensure that the more junior personnel on operations are compensated for their tax bill while deployed.

The forces' pay award was significantly higher than other public sector groups, including the police and prison officers, who have had a 1.9% rise imposed. The MoD says the higher award for service personnel is in recognition of the pressure they are under fighting two counter-insurgency campaigns in Afghanistan and Iraq.

Defence Minister Bob Ainsworth later sought to pour scorn on the LibDems' number crunching and said he was writing to Mr Cable accusing him of a "Herculean distortion of the facts" and calling on him to retract his claims.

He said: "It is misleading and irresponsible in the extreme for you to use our armed forces as a political football in this way."

Tory leader David Cameron stepped up his attack on the change, which he hopes to make a key feature of his local election campaign. The removal of the 10p rate for the lowest paid, which came into effect yesterday, was "kicking people when they are down," Mr Cameron said.

Prominent Labour figures also attacked the change, with former Welfare Reform Minister Frank Field claiming there was "growing unease" within the party.

The Commons Treasury Select Committee said low paid workers without families would be hardest hit by the changes, which were announced in last year's Budget.

The Prime Minister said in Oxford that the increase in child benefit, child tax credit and the winter fuel allowance meant that overall people would be better off. He also criticised the Conservatives, saying they were making "false promises" to the public.

There was increasing unrest among Labour ranks over Mr Brown's abolition of the 10p starting rate of income tax, after a powerful cross-party committee of MPs branded it "unreasonable".