Boris Johnson faced embarrassment last night after it emerged that he once mocked the “obsession” of women aid workers with ending female genital mutilation — days before he plans to parade his anti-FGM credentials.

Johnson will appear on Tuesday with Nimco Ali, the anti-FGM campaigner, at the screening of a film on the issue.

A rival leadership camp drew attention to an article Johnson wrote for The Spectator magazine in 2002, which ridiculed efforts to combat the problem and said colonialism was a good thing.

After a trip to Uganda, he wrote: “Almost every dollar of western aid seems tied to some programme of female emancipation — stamping out clitorectomy, polygamy, bride-price, or whatever.

“And while some readers may feel vaguely that the African male