Iain Duncan Smith resigns as Work and Pensions Secretary over 'indefensible' benefits cuts

In an excoriating parting shot at the Chancellor, the Work and Pensions Secretary complained of pressure to "salami slice" welfare and a failure to spread the burden of spending curbs.

"I have for some time and rather reluctantly come to believe that the latest changes to benefits to the disabled and the context in which they've been made are, a compromise too far," Mr Duncan Smith wrote in his resignation letter.

"While they are defensible in narrow terms, given the continuing deficit, they are not defensible in the way they were placed within a Budget that benefits higher earning taxpayers. They should have instead been part of a wider process to engage others in finding the best way to better focus resources on those most in need.

"I am unable to watch passively whilst certain policies are enacted in order to meet the fiscal self imposed restraints that I believe are more and more perceived as distinctly political rather than in the national economic interest."

Mr Duncan Smith has been at loggerheads with David Cameron and Mr Osborne over whether Britain should stay in the EU, joining a handful of other Cabinet ministers in calling for Brexit.

But his letter to the Prime Minister indicated that the row over cuts to the Personal Independence Payment (PIP) had been the last straw.

His announcement came after the Treasury signalled an humiliating climbdown over the plans to change PIP assessment criteria, which were expected to slash around £1.3 billion a year off the cost.

Government sources said they wanted to kick the shake-up - initially announced by the Department for Work and Pensions last week - "into the long grass" and were not "wedded" to the savings figures that featured in the Budget.

Mr Duncan Smith said he was "incredibly proud" of the welfare reforms he had overseen over the past five years.

"Throughout these years, because of the perilous public finances we inherited from the last Labour administration, difficult cuts have been necessary," he said. "I have found some of these cuts easier to justify than others but aware of the economic situation and determined to be a team player I have accepted their necessity.

"You are aware that I believe the cuts would have been even fairer to younger families and people of working age if we had been willing to reduce some of the benefits given to better-off pensioners but I have attempted to work within the constraints that you and the Chancellor set."

In a particularly cutting passage, Mr Duncan Smith cited a phrase often used by Mr Cameron and Mr Osborne, stating: "I hope as the government goes forward you can look again ... at the balance of the cuts you have insisted upon and wonder if enough has been done to ensure 'we are all in this together'."

Mr Duncan Smith said "the advancement of social justice" had been his motivation for taking the job as Work and Pensions Secretary.

He was praised by Tory MP and fellow Brexit campaigner Peter Bone, who said: "IDS has always been a man of conviction! Tonight, yet again he put the country first."

Andrew Percy, who had led a Conservative backbench revolt against the PIP cuts, wrote on Twitter: "Credit to IDS. I'll say no more tonight but all is not as it has seemed in the past few days."

But a number of Labour MPs insisted Mr Duncan Smith's departure was driven by the EU referendum battle.

Former frontbencher Chuka Umunna said: "IDS resigning has everything to do with the EU and nothing to do with welfare - why wait this long after causing misery to so many to resign."