And in an interview for GQ magazine with Piers Morgan he also admits finding Cherie Blair sexually attractive.

The shadow education minister previously admitted trying the Class A drug. But he has said that none of it went up his nose because he sneezed.

Now Mr Johnson, 42, admits some may have gone up his nose. He tells Morgan: "I tried it at university and I remember it vividly. And it achieved no pharmacological, psychotropic or any other effect on me whatsoever."

Asked whether cocaine went up his nose despite the sneeze, Mr Johnson replied: "It must have done, yes, but it didn't do much for me I can tell you."

Asked about cannabis, he told the magazine: "There was a period before university when I had quite a few (cannabis joints). But funnily enough, not much at university. It was jolly nice. But apparently it is very different these days. Much stronger. I've become very illiberal about it. I don't want my kids to take drugs."

The MP, who was sacked from the front bench by ex-leader Michael Howard for lying about an affair, has made a series of high-profile blunders.

He was famously sent to Liverpool to apologise after accusing the city of wallowing in grief over the execution of Iraq hostage Ken Bigley. He was in hot water again in April after insulting the city of Portsmouth.

He told GQ: "I love Norwich. And Portsmouth. And Liverpool. It's all nonsense. I said about Portsmouth that there was too much drugs, obesity and underachievement. And there is. It's a statistical fact. Why shouldn't I be allowed to say that? Then, to top it all some local bloke went on the radio and called me fat."

Asked whether he could imagine having sex with the Prime Minister's wife Cherie Blair, he says in the interview: "I could, yeah. No, don't put that in! God! Not me."