ALLEGATIONS Theresa May let David Cameron down over Brexit have been rubbished by Iain Duncan Smith.

The Chingford and Woodford Green MP urged Remainers to do the “grown-up thing” and “get behind Theresa May” instead of picking apart the failed bid to remain within the EU.

In a statement to the BBC, the former Work and Pensions Secretary addressed a book released by David Cameron’s former director of communications, Sir Craig Oliver.

Sir Craig said in ‘Unleashing Demons: The Inside Story of Brexit’ the current Prime Minister was seen by some as an “enemy agent” during the EU referendum.

In his book, which Sir Craig said was attempt to explain “what went wrong”, he claimed Mrs May failed to back the Remain campaign 13 times.

Mr Duncan Smith said: "In the past, a knight of the realm who had failed in battle and lost would have quit the field and retired in humility to better understand their own failings.

"How surprising then to find that far from that, Sir Craig Oliver, one of the leading lights of Remain, has decided to instead try to pin the blame for his failure on others, particularly the new prime minister.

"Craig Oliver's is one of a growing number of foolish attempts by ex-government Remainers who lost to shift responsibility for their failure.

"The grown-up thing for them to do, instead of carping, is to show some humility and get behind Theresa May as she seeks to get back control of migration with the EU as we leave."

In response, Sir Craig said his book was a “sincere and honest attempt” to explain Remain’s failure and Mr Duncan Smith had got the "wrong end of the stick".