But he refused to offer concessions to Labour's backbench social security committee. On Monday, the Government faces its biggest revolt since the general election when its Welfare Reform Bill is debated by the Commons.
Mr Darling said: "The reforms are right in principle and part of a coherent approach to welfare reform. They are the right thing to do and that is why we will press on."
Government sources insisted there had been wide consultation over the shake-up of disability benefits, and played down the rebellion. The Social Security Secretary stressed that under the legislation there would be extra money for the most severely disabled and a disability income guarantee.
No one on benefits at the point of transition to the new system would get their benefits cut and other key government measures such as the working family tax credit and the New Deal would ensure work paid.
Special rules would be introduced so that people on incapacity benefit would not lose out if they tried a job that did not work out, he added.
"We will make sure incapacity benefit goes to the people it was originally intended for ... we will recognise the huge growth in occupational pensions and strike a fair partnership between state and occupational help for people who retire early onto benefit."
But Frank Field, the former social security minister, said "disquiet" among backbenchers covered an even larger number than the 40 who have already put down amendments reversing the cuts in entitlement to incapacity benefits.
MPs feared the severe disablement allowance and widow's benefits for older women would be abolished for most. Mr Field said the cuts would take up to pounds 1.3bn from people.
He added: "We are talking about cuts, or abolishing entitlement to benefits which people have earned over 30 years or more. It is in total opposition to what the Government says it wishes to do."Reuse content