Conservative MP Bob Blackman, who recently suggested David Cameron should resurrect Section 28, previously had an affair behind his wife’s back for 11 years, according to his former mistress.

Carol Shaw, a councillor in Brent, north west London, was so incensed with the MP’s anti-gay comments in relation to the government’s intention to introduce same-sex marriage that she decided to go public about his infidelity.

Earlier this month, Mr Blackman, who represents Harrow East in north west London, responded to David Cameron’s support for religious same-sex marriages by suggesting the prime minister should resurrect Section 28, a notorious piece of anti-gay legislation passed under the Thatcher government.

It banned the “promotion” of homosexuality in schools and was repealed by Tony Blair’s government in 2003.

Mr Blackman went on to say of how marriage is “between one man and one woman” and then stated that re-introducing Section 28 would be more appropriate than pushing ahead with marriage reform.

Tony McNulty, Harrow East’s former Labour MP responded by tweeting that Mr Blackman was a “complete idiot!!”

Speaking of Mr Blackman’s comments, Ms Shaw told the Sunday Mirror “I couldn’t believe a man who had an affair with me for over 11 years could have the cheek to preach about the sanctity of marriage.

“You have to be squeaky clean to do that and he has made a mistake”.

She continued: “Bob is an absolute hypocrite. He talks about marriage being between one man and one woman… but why does he not practice what he preaches?

“More than once I asked about his wife and I got the impression one day he might leave her, because he said he could love two people at the same time.”

When the Sunday Mirror tried to quiz Mr Blackman about his relationship with Ms Shaw, he refused to comment, angrily saying: “I don’t wish to speak to you.”

Mr Blackman – who proudly displays photos of himself with David Cameron and London Mayor Boris Johnson on his website – ­married his wife Nicola in 1988.

Ms Shaw, Mr Blackman and his wife worked on Barnet Council when the affair started.

The affair ended in 2000.