An MP who backed Theresa May’s opponent in the Tory leadership race, believes she faces a “huge task” as PM to unify the country post-Brexit.

MP for Chingford and Woodford Green, Iain Duncan Smith, said he “unreservedly congratulates” Mrs May after Andrea Leadsom’s surprise exit from the Conservative leadership race on Monday (July 11).

The Home Secretary is set to become the country’s second female leader today (July 13) after David Cameron has his final Prime Minister Questions in the House of Commons.

Mr Duncan Smith said he was “deeply concerned” after “the concerted and brutal attempt to destroy [Mrs Leadsom’s] character”.

The Tory candidate faced criticism over the weekend after she appeared to suggest having children gave her an advantage over Mrs May, who has none.

Mr Duncan Smith admitted “even by the low standards of Westminster” it was “painful”.

He added: “The Andrea Leadsom I and many in Parliament know is a decent, hard-working and compassionate woman.

“I deeply regret that these attributes were tossed aside, as low and personal politics took over.”

The former minister has known the future PM Mrs May for a large part of his time in politics, appointing her the first female Conservative Party chairman when he was leader.

He added: “I know her to be hard-working, conscientious and thoroughly decent and I unreservedly congratulate her.”

The former PM said he is “optimistic” for the country making a success outside the EU but Mrs May “faces three huge tasks” in delivering it.

He said: “The first is unifying the Government and the country. The second is taking the UK out of the EU and the third is to rebalance the economy and rebalance society.

“‘Leave must mean leave’ is an easy phrase, but to achieve it there needs to be some substance to our red lines and, importantly, a clear idea of the process by which we will implement the decision of the British people.”