Rory Stewart said that while he served in Government there were "situations of male prisoners selfidentifying as females then raping staff in prison".
The former Tory MP, who ran in last year's leadership contest, made the remarks in GQ as he was interviewed as part of his candidacy for Mayor of London.
When asked whether anyone who identifies as a woman should be allowed to go into female-only spaces such as toilets, Mr Stewart said: “I’m instinctively worried about that, partly because when I was prisons minister, we had situations of male prisoners selfidentifying as females then raping staff in prison.