Gordon Brown faced new threats of resignations from his government this weekend as the rebellion over his decision to scrap the 10p income tax band escalated.

Yesterday five more ministerial aides broke cover to criticise his decision, with one declaring publicly that he is considering quitting. Others are known to be threatening to resign.

Amid signs of panic and confusion within the Treasury, the prime minister was also hit by the unprecedented leak of a secret file drawn up by his own whips about rebels opposing his terror reforms. The document shows that more than 50 MPs, including 10 former ministers, are expected to vote against government plans to allow detention without trial for 42 days.

The file reveals that even backbenchers and members of the government who are prepared to vote for the changes privately believe that the proposals are “barmy” and “plucked out of thin air”. At least one government minister and six ministerial aides have grave concerns about the measure.

The immediate crisis facing Brown centres on his abolition of the 10p tax rate, a move which has left more than 5m of the poorest households in Britain worse off. He is becoming increasingly frustrated by the controversy, privately claiming that the critics are wrong. Behind the scenes last week he is said to have been shaking with anger while defending the measure, blaming his own backbenchers for failing to explain the policy more effectively to their constituents.

Five ministerial aides publicly criticised the policy last week while a sixth, Angela Smith, was prevented from resigning only after a personal appeal from Brown. Yesterday five more parliamentary private secretaries (PPSs) joined the attack. Several others are voicing serious concerns in private.

Derek Wyatt, a junior aide to Margaret Hodge, a culture minister, said: “I’ve had virulent e-mails from my constituents saying they feel betrayed and deserted. They say they will never vote for Labour again. I have thought about resigning, yes. The government has time yet, so it’s too early to say. But I’ve taken soundings from my local party and yes, many of us do feel this is a betrayal of our core beliefs.”

The Institute for Fiscal Studies calculates that the biggest losers from the policy are those earning between about £5,000 and £18,000. Worst affected are single working people without children, low-earning couples without children and tax-paying women between 60 and 64 - groups which do not benefit from tax credits.

Wyatt, the MP for Sittingbourne and Sheppey, said: “That is serious. It’s not what this party is meant to be all about. I have no time for the idea [that] this can’t be fixed.”

Another PPS labelled the decision to scrap the 10p rate as a “bizarre mistake”. In a sign of Brown’s diminishing authority, two aides publicly questioned the entire thinking behind the budget.

Russell Brown, a junior aide to Des Browne, the defence secretary, said: “We’ve got to find a way to sort out this mess. We need to take this whole fiscal package, which was meant to be revenue neutral, and put it back together again. Questions will be asked as to how the government got it so badly wrong.”

John Mann, an aide to Tessa Jowell, the Olympics minister who has herself called for a rethink, said: “I’ll be making my case very strongly and forcefully to the chancellor at the next budget. A good budget should reward work. Some people on low incomes have lost out this time and I hope we can put that right at the next budget. The 10p tax rate is not the only issue, there are also taxable allowances and finances that need to be looked at as part of the package.”

The abolition of the 10p income tax rate, which came into effect this financial year, was announced by Brown in his last budget; at the time it was masked by his trumpeting of a 2p cut from the basic rate of income tax. It comes as the government has offered concessions to wealthy “nondoms” after an outcry from them.

The 10p measure will be debated in the Commons on Monday, with a crunch vote the following week. Alistair Darling, the chancellor, hopes to avoid a humiliating defeat by persuading rebels that he will change the policy as soon as the global economic situation allows. Yesterday Yvette Cooper, his chief secretary, defended the policy, insisting the government was doing everything possible.

However, Rob Marris, an aide to Shaun Woodward, the Northern Ireland secretary, said: “I hope the government has a rethink and looks at ways to compensate those who have been adversely affected by these measures. There’s no need to wait until the next budget.”

Another PPS said he regarded the controversy as a “core issue” and would consider resigning if no concessions are made. Angela Eagle, the junior Treasury minister, has suggested that the government might review the policy; two government figures linked to the Treasury have privately expressed their concerns to The Sunday Times, adding to the impression of a split inside the Treasury itself.

Last night Darling’s aides denied that his own team were unhappy. A spokeswoman said: “He has not had a single representation from anyone in the Treasury about the policy.”

However, a senior Labour peer warned that the government was in deep trouble over the measure. Lord Lipsey, an economist, said: “Any government that loses the power to set taxation is finished. There is no way of getting out of this that is a) affordable, b) workable and c) avoids total humiliation.”

David Miliband, the foreign secretary, admitted Labour is now the "political underdog," adding: "We need to put up a fight."

Many backbenchers fear the issue has the potential to become as damaging to the party as the fallout from the infamous 75p rise in pensions in Brown’s budget of 1999. The derisory increase caused a ferocious backlash from pensioners and Brown was subsequently forced to spend billions repairing the damage with measures such as the winter fuel allowance.

One crumb of comfort for Brown is in a new poll for The Sunday Times on the London mayoral election. The survey, conducted by the company Mruk Cello, shows Ken Livingstone in a narrow 45%-44% lead over Boris Johnson.

Additional reporting: Chris Gourlay

Times Recommends

• Times Christmas appeal: Letter from the Editor
• Conferences — what a waste of money
• Schools supremo learns a painful lesson