In a series of votes, MPs opposed changes under the Welfare Reform and Pensions Bill, with as many as 54 voting against the Government.
The row centred on three clauses of the Bill's disability benefit provisions, the limit of IB to people who have been in recent employment; the introduction of means-testing IB for people with pension income; and the abolition of the severe disability allowance.
Backbenchers were also likely to support the peers who defeated proposals on pension reform, including changes to war widows and the bereavement allowance.
Opening the debate, Mr Darling, the Secretary of State for Social Security, made last-minute concessions to backbenchers, insisting that the Government had the interests of the disabled at heart.
"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.
"We want to do more for the many people disabled from birth and from childhood who have got no chance to work and who have got no chance to make National Insurance contributions."
But Roger Berry, the MP for Kingswood, moving the rebel amendment, insisted that continued opposition to the proposals was the only way to ensure a Bill that all Labour MPs could be proud of.
Even with the revised thresholds proposed by Mr Darling, at least 310,000 people unable to work would "lose out under the proposals".
"To put it simply, the Government's proposals will reduce benefits for disabled people unable to work. These are people who have had a work test, have paid their National Insurance contributions and have been declared unfit to work.
"I feel I have no alternative but, with very great regret, to vote against the Government's motion and I would urge other Members to do the same."
Tom Clarke, a former spokesman on the disabled, said if the Bill was passed in its present form, "many people would find themselves significantly poorer".
The MP for Coatbridge and Chryston said: "We are talking about people's incomes being in effect taxed at a rate which not one person in the land - not even the richest millionaire - is normally asked to pay.
"Those who expected more from our Government do feel deeply betrayed. The truth is - and I very much regret to have to say this to you - there is no popular support for this," he told ministers.
Supporting the Government, Sam Galbraith, the MP for Strathkelvin and Bearsden, another former Labour minister and registered disabled himself, said: "This idea that somehow or other the contributory principle is a inviolate thing that must never be touched cannot any longer be true. This may have been true in the early days when the welfare state was set up but is not the case today."
Audrey Wise, the MP for Preston, said: "It is we who are able-bodied and healthy who should pay the whole cost of funding improvements for disabled people.
"I don't believe there is any disabled person who is in too good a position in our country at this time." Mrs Wise said many rebel Labour MPs had "twittered" that they would be voting in the same lobby as Tories.
But she reminded the Social Security minister Jeff Rooker how the two of them voted alone against the 1977 Labour government's plans to increase the tax threshold at least in line with inflation.
In an intervention, Mr Rooker said: "The reason we did it - because we intended to try to defeat the government - not just as a token, as a bleeding heart on our sleeve, it was because the government had flatly refused to move or listen at any time during the discussions we had with them. That does not apply to this Bill."
But urging Labour MPs to vote against the measure, Ms Wise added: "You can do this and you will improve the Government's policies and you can live perfectly happily with a clear conscience."
David Willetts, the Tory spokesman on Education, attacked the means-testing proposals as being "hitherto unknown" in the social security system. "It is not a means test that takes account of people's incomes in general. It simply takes account of one form of income. It only penalises you if you have an occupational or a personal pension."
Dr Lynne Jones, the Labour MP for Birmingham Selly Oak, added that in Opposition the Labour front bench had supported the "sheer thrift and foresight" of people taking out personal pensions, whereas the reforms would now penalise that "same group".
Labour MPs who voted against goverment plans for means-testing incapacity benefit in the Welfare Reform and Pensions Bill:
Diane Abbott (Hackney N and Stoke Newington), John Austin (Erith and Thamesmead), Harry Barnes (Derbyshire NE), Tony Benn (Chesterfield), Andrew Bennett (Denton and Reddish). Dr Roger Berry (Kingswood). Ronnie Campbell (Blyth Valley), Martin Caton (Gower), David Chaytor (Bury North), Michael Clapham (Barnsley West and Penistone), Tom Clarke (Coatbridge and Chryston), Tony Clarke (Northampton South), Ann Clwyd (Cynon Valley), Michael Connarty (Falkirk E), Jeremy Corbyn (Islington N), Jim Cousins (Newcastle Upon Tyne Central), John Cryer (Hornchurch). Tam Dalyell (Linlithgow), Ian Davidson (Glasgow Pollock), Denzil Davies (Llanelli), Jim Dobbin (Heywood and Middleton), Gwyneth Dunwoody (Crewe and Nantwich). William Etherington (Sunderland N), Frank Field (Birkenhead), Paul Flynn (Newport W). Neil Gerrard (Walthamstow). Dr Ian Gibson (Norwich N), Dr Norman Godman (Greenock and Inverclyde), Kelvin Hopkins (Luton N), Eric Illsley (Barnsley Central). Dr Lynne Jones (Birmingham Selly Oak), Terry Lewis (Worsley), Ken Livingstone (Brent E), John McAllion (Dundee E), John McDonnell (Hayes and Harlington), Dr John Marek (Wrexham), David Marshall (Glasgow Shettleston), Robert Marshall-Andrews (Medway), Bill Michie (Sheffield Heeley), Julie Morgan (Cardiff N), Denis Murphy (Wansbeck), Gordon Prentice (Pendle), Ted Rowlands (Merthyr Tydfil and Rhymney). Brian Sedgemore (Hackney S and Shoreditch), Alan Simpson (Nottingham S), Dennis Skinner (Bolsover), Llewellyn Smith (Blaneau Gwent), Desmond Turner (Brighton Kemptown), Robert Wareing (Liverpool West Derby). Betty Williams (Conwy), David Winnick (Walsall N), Audrey Wise (Preston), Mike Wood (Batley and Spen), Tony Worthington (Clydebank and Milngavie)