Labour leader Jeremy Corbyn has criticised Andrea Leadsom's controversial motherhood comments about Theresa May.
"She [Leadsom] shouldn't be raising it as a way of criticism, it shouldn't raised as a matter of public debate," he said in an interview with ITV News.
"A man would never be asked those questions - why should a woman be asked those questions?"
They are both putting themselves forward for leadership of their party, it's up to them to have what I hope will be a serious, intelligent and mature debate about the policies each would wish to follow as leader, not reduce it to this sort of level of personal criticism, it's unfair and it's wrong.
Duncan Smith told Peston on Sunday that there had been "a black-ops" operation to destroy her reputation.
Leadsom's suggestion that being a mother would make her a better prime minister has sparked an almighty row - read exactly what she said.
A major row has erupted after Andrea Leadsom allegedly said being a mother makes her a better choice for prime minister than Theresa May.