Andrea Leadsom facing 'black-ops campaign' to discredit her says Iain Duncan Smith

"I've seen it all before - the reality is that both of them are qualified.

"Look, if Andrea was so unqualified to be Prime Minister, and you know we've had a lot of sniping, a kind of real 'black-ops' operation to denigrate her reputation.

"If she was so bad what in heaven's sake would the Prime Minister be doing making her a serious government minister?"

He later added: "We should really be very careful about the threats and the things that we say, all of us, and conduct this in decency."

Ms Patel, who is backing Mrs May's campaign, warned that Mrs Leadsom could find herself unable to govern due to the lack of support from MPs, or win an election victory by appealing to swing voters.

Mr Duncan Smith added that Ms Leadsom's controversial interview with the Times where she claimed she would be a better Prime Minister than Theresa May because she had children was a stitch up.

He said: "I've been around in politics long enough to see plenty of incredibly experienced cabinet ministers and Prime Ministers get stitched up in the course of an interview..."

He added: "The question really was did Andrea at any stage really believe that she was in the business of trying to contrast her family background with Theresa's and I don't believe that.

"I've talked to her, she's actually mortified about that, really genuinely mortified."