Boris Johnson has admitted he took cocaine when he was a teenager, but insisted he has not done it more than once.

In an interview with BBC Radio 4′s World at One programme on Friday, Johnson said it was “a single inconclusive event that took place when I was a teenager.”

Asked if he had taken it again since then, Johnson said: “No.”

It comes after Michael Gove’s rival leadership bid was knocked off course after he confessed to having used the drug.

Johnson had swerved questions at his leadership campaign launch earlier this week about his past drug use.

He admitted to drug use in the past including in a 2007 interview with GQ.

Piers Morgan: What did you think of Cameron standing his ground over the drugs issue and refusing to say whether he had ever taken them? 

Boris Johnson: I thought he was right. I’m not a great drug man myself. 

PM: You once alluded to the fact that you tried cocaine but sneezed on it. 

BJ: Yes. I tried it at university and I remember it vividly. And it achieved no pharmacological, psychotropical or any other effect on me whatsoever. 

PM: Some of it did creep in to your big hooter, then, despite the sneeze? 

BJ: It must have done, yes, but it didn’t do much for me, I can tell you.

In a 2008 interview with Marie Claire magazine, Johnson was also asked if he had ever taken cocaine.

He said: “Well, that was when I was 19. It all goes to show that sometimes it’s better not to say anything. I thoroughly disagree with drugs. I don’t want my kids having drugs.”

In a 2005 appearance on Have I Got News For You Johnson also said: “I think I was once given cocaine, but I sneezed and so it did not go up my nose. In fact, I may have been doing icing sugar.”