Having re-watched that episode of Have I Got News For You last night on you tube I can confirm you are wrong, Boris did not admit to snorting cocaine he admitted only that he "had tried to snort cocaine but failed" when he sneezed blowing the cocaine away... That in my opinion does not constitute admitting that he snorted coke at any point.
I still think he's as nuts as they come, Livingstone may be a traitor but what if it's a case of the "traitor" Livingstone or the complete crazyman that is Boris? Ever heard the phrase "better the devil you know"? well I think this is a good time to admit that it could turn out to be a case of this phrase needing to be said if he does win. Regardless I'd rather a 3rd person ran for mayor with any real hope of succeeding who was not too liberal/conservative/puppeteered/extremist of any wing ran and therefore provided with a SANE better alternative from Livingstone.