But the backbench revolt on disability benefits was lower than expected and did not defeat the government. Social Security Secretary Alistair Darling said: "Ministers are well pleased with the result."

MPs voted to overturn House of Lords amendments to the Bill dealing with means-testing and eligibility for incapacity benefit.

In two separate votes MPs polled 325 to 265, giving the government a majority of 60, and 320 to 262, a government majority of 58.

The BBC's Niall Dickson: "The government may not be beaten but it has been bruised"

Speaking after the first vote Mr Darling said: "The rebellion is down to 53.

"This sends a clear message to the Lords. The government intends to see this Bill through."

In May, when the Bill was last debated in the Commons, 67 Labour backbenchers voted against the government.

Despite fewer Labour rebels the government's problems with the Bill are by no means over as the legislation may be thrown out by the Lords next week.

Lord Ashley: "The rebels won the argument"

Labour peer Lord Ashley has already said he will reinstate the amendments when the Bill returns to the Lords on Monday.

He said: "I think the rebels in the Commons won the moral argument."

Turning to the compromise offered by the government on incapacity benefit earlier in the week, the Labour peer said: "The piffling concessions by the government have had no visible impact on the House of Lords.

"If the Bill is lost, it's the responsibility of the government whose behaviour was inexcusable."

The reforms must make their passage through both houses of Parliament within the next two weeks or the entire piece of legislation will fail.

Constiutional battle

But whatever resistance the government encounters in the Lords Mr Darling remains determined to get the Bill passed. He told BBC Two's Newsnight programme: "At the end of the day it becomes a constitutional matter.

"The House of Lords has to accept that we are the elected chamber."

Ministers have previously warned that if the Lords obstruct key legislation, they will abandon the compromise that would see 92 hereditary peers keep their seats in a reformed upper house.

MPs also overturned several other Lords amendments to the Bill, including one aimed at ensuring Armed Forces widows keep their pensions if they remarry and another extending from six months to two years the payment of bereavement allowance.

The Labour rebellion came despite concessions offered by Mr Darling at the beginning of the week when he raised the threshold at which people start to lose IB from �50 a week of pension income to �85.

In another amendment he altered the original plan for anyone who had not made National Insurance contributions in the previous two years to be denied incapacity benefit. Mr Darling extended that to three years.

But MPs and campaigners for the disabled said that regardless of the changes, many disabled people would still lose out under the Bill's measures.

Commons clashes

Mr Darling opened the Commons debate saying that the government had the interests of the disabled at heart.

But Labour rebels argued that the Bill would penalise many disabled people, and discourage saving.

Mr Darling defended plans to introduce means-testing on incapacity benefit for those who receive separate income from a pension.

He said: "The first thing we are doing in our reforms is to do more for people who need it most.

"Right now the system simply isn't doing enough and this Bill starts to put that right."

Blair backs reforms

Earlier, Tony Blair defended his social security secretary's reforms during Prime Minister's Questions.

Mr Blair said Labour had promised to reform the welfare state before coming to power and added: "I believe the reforms that we are introducing are the right reforms."

The prime minister told MPs the changes were necessary as the number of people claiming incapacity benefit had trebled since 1979, and the measures contained in the Bill "will not affect any existing claimants".

Roger Berry: The changes are a "blot on Labour's record"

During the debate Mr Darling's Tory shadow, David Willetts, attacked the government's decision to means-test incapacity benefit, calling it "a bizarre route to go down for a government that claims it wants to encourage occupational pension provision".

Former Labour minister Tom Clarke made clear his determination to oppose the Bill for the second time, saying it would act against the government's own desire to reward savings.

He said means-testing would lead people to ask: " Why save when you know the benefits to which you are entitled are going to be cut?"

Dr Roger Berry, another long-standing Labour opponent of the government's plans, said: "More means-testing further reduces the incentive to save, reduces benefit take-up, and encourages dishonesty and is very costly to administer."