Tory MP Boris Johnson has admitted to smoking cannabis and snorting cocaine, but few of his Oxfordshire colleagues shared his candour when approached last night.

The Henley MP tore up Tory leader David Cameron's carefully crafted rulebook on dealing with youthful narcotics indiscretions as he told how he tried the class A drug but said it had no effect on him, and that he had often smoked cannabis.

Witney MP Mr Cameron and Andrew Smith, Oxford East Labour MP, both refused to follow Mr Johnson's lead last night.

Evan Harris, MP for Oxford West and Abingdon, however said he had never tried either drug.

In a frank interview with this month'sGQ magazine, Mr Johnson said: "I tried it (cocaine) at university and I remember it vividly. It achieved no pharmacological, psychotropic or any other effect on me whatsoever."

Mr Johnson had previously said, on TV show Have I Got News For You, that he was once given cocaine but sneezed "so it did not go up my nose".

In the GQ interview, asked by former Daily Mirror editor Piers Morgan whether some of the powder crept into 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 if he had tried any other drugs, Mr Johnson responded: "Cannabis, you mean? Yes, I have. There was a period before university when I had quite a few spliffs.

"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 Oxford Mail asked the county's MPs if they would follow Mr Johnson's lead, but Mr Cameron's spokesman said: "We have nothing further to add. It's exactly as it was. No comment on his life before going into politics."

Labour MP Mr Smith also said: "I have always and consistently declined to comment on this."

Liberal Democrat MP Mr Harris said: "I didn't take cocaine or cannabis but the question for Conservative Party politicians is why their policy is to give criminal records to all young people who experiment with these drugs while either having done it themselves or even worse, in the case of David Cameron, refusing to give a straight answer.

"Tory policy, trying to appear tough on drug-taking, does not permit a defence of youthful indiscretion so Boris Johnson really has to explain why he is not seeking to prosecute himself to the full extent of the law that he wishes to impose on everyone else."

Banbury MP Tony Baldry was abroad on Parliamentary business and could not be contacted last night. Wantage MP Ed Vaizey was also unavailable.

Ann Ducker, president of South Oxfordshire Conservative Association and leader of South Oxfordshire District Council, dismissed Mr Johnson's admission with a laugh. She said: "It was all a long time ago and he is very much against drugs now. We will certainly not be asking for his resignation or anything like that."

But anti-drugs campaigner Anna Nichols from Didcot, who is running courses on how to "drug-proof" children, was not happy.

She said: "Yet another high profile person admitting to using drugs points again to the fact that so many across all walks of life experiment with illegal drugs. Boris and his family were fortunate it did not progress beyond experimentation."