Jeremy Corbyn has accused Iain Duncan Smith of "hiding his conscience" for six years, and urged his successor to U-turn on proposed cuts.
The Labour leader said former Work and Pensions Secretary Duncan Smith, who resigned last night, had presided over some "fairly appalling policies".
He added that the first task of Duncan Smith's replacement, Stephen Crabb, was to completely reinstate Personal Independence Payments.
Corbyn said his party would "hold the Government to account" over PIP, and described current availability to work tests as "appalling".
This is a man who has presided over so much, that has been so damaging to the lives of so many people with disabilities. He's taken so much away from people with disabilities.
He's suddenly found a conscience now - I wonder where the conscience has been hiding for the past six years.
Iain Duncan Smith tells ITV News' Robert Peston his resignation was intended to push the government into pursuing a fairer welfare policy.
Former Work and Pensions Security accuses government of making 'arbitrary cuts' which he says damages the party and the country.
Conservatives fractures show with claim and counter-claim by ministers from within the DWP about the conduct of Iain Duncan Smith.