Iain Duncan Smith has said he is resigning as work and pensions secretary, complaining of pressure from the Treasury to cut benefits.

The senior UK Government minister made the announcement on Friday evening.

In a letter to the Prime Minister, he said he felt policies were being carried out for political reasons rather than in the national interest.

He said: "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.

"Too often my team and I have been pressured in the immediate run up to a budget or fiscal event to deliver yet more reductions to the working age benefit bill.

"There has been too much emphasis on money saving exercises and not enough awareness from the Treasury, in particular, that the government's vision of a new welfare-to-work system could not be repeatedly salami-sliced."

Calling the latest changes to benefits "a compromise too far", he said: "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."