THREE of Scotland's political leaders have admitted taking cannabis, while Labour's Jim Murphy said he couldn't remember if he ever sniffed glue while growing up.

SNP First Minister Nicola Sturgeon, Scottish Conservative leader Ruth Davidson and Liberal Democrat leader Willie Rennie told students at a debate at the University of Glasgow that they had tried cannabis in their youth, after being questioned about their policy on decriminalising the drug.

Mr Murphy, who is teetotal, said that "glue sniffing was the thing" in the Glasgow housing estate he grew up in. When asked whether he had tried it, he replied: "I don't remember", before adding: "At that time, drugs, and I'm giving away my age, it was just a kind of working class thing to do, kind of sniffing glue out of crisp pokes. It was a dreadful, harmful thing that was in that community at the time."

A spokesman for Scottish Labour later said that the party leader had "never taken drugs" and that he had been making the point that "when he was growing up drugs weren't as widespread and that the harmful thing for many people back then was glue sniffing." He added: "For the record that's not something Mr Murphy has tried either."

The leaders were commenting on research by the Institute for Social and Economic Research which said up to £900 million a year could be raised through taxation of a regulated cannabis market, and were later asked if they had tried the drug.

Ms Sturgeon said: "I'm actually on record as making an admission on this once, probably, possibly at this university although not at this union, but it made me awfully sick."

Mr Rennie said: "Yes, in my youthful days" while Ms Davidson responded by saying: "I went to Buckhaven High School, what do you think? I'm with Nicola, once or twice and it made me feel really sick."

Former Lib Dem minister Norman Baker resigned from the Home Office in November, claiming Home Secretary Theresa May suppressed proposals to reform drugs policy.

Mr Rennie said it was a "despicable" decision and called for an open debate on drug use in the UK "based on facts and science".

Ms Sturgeon and Mr Murphy echoed his call for an open debate on drugs but said cannabis should not be legalised, citing evidence linking it to mental health problems.

The First Minister said: "I think where Willie is right is that you should always trust the public to have grown up, evidence based debates, and I definitely don't think suppressing evidence on issues like this helps a debate like this at all."

Ms Davidson said: "I think some things are worth more than money, and the health of our nation is one of them."

The debate, at the university's Queen Margaret Union on Thursday night, was the first time that Mr Murphy had faced other Scottish party bosses in a public debate as Labour leader, with his status as an MP meaning is yet to enter the Holyrood chamber.