Bishop Holloway, the Primus of the Scottish Episcopal Church, agreed with the Liberal Democrat leader Charles Kennedy's call for a Royal Commission on drugs.

The bishop went further by saying cannabis should be decriminalised, that young people should be taught how to use drugs responsibly and that he had tried cannabis .

Strathclyde Police Chief Constable John Orr: "Zero tolerance is the answer."

Strathclyde Police Chief Constable John Orr said there was evidence to prove cannabis users moved on to harder drugs.

"I think any simplistic view that suggests cannabis is something you can put to the side and say is not dangerous is something we would say you need to be very careful about," Mr Orr told BBC Radio Scotland.

Speaking for the Chief Constables' Crime Committee Mr Orr said he was worried children were getting mixed messages on drugs and that any debate could further muddy the waters.

'Not helpful'

He added: "People who are cannabis users, pervasive cannabis users as I describe them, actually start popping pills and doing other things as well.

"It's a small number of people who apparently have the robustness of their own personality to just adhere to a joint of cannabis."

Heroin use results from softer drugs, the police say

In response to Bishop Holloway's comments, Anne Allan of the Board of Social Responsibility of the Church of Scotland described his remarks as "not helpful", but added that those convicted of recreational use needed treatment rather than a criminal record.

However, the Scottish Parent Teacher Council supported the call for a proper, open debate.

Spokeswoman Judith Gillespie said it was important that children were given the right information about the consequences of drug taking.

Scotland Against Drugs, the anti-drugs pressure group, condemned the bishop's comments.

"It's important that people in the public eye should make statements like this with very carefully considered thought," said SAD Director Alasdair Ramsey.

"Someone in his position expects to have people in his flock follow what he says.

Lords report

"People like the bishop should be very prudent about their comments, especially regarding drugs, as the way it will be picked up by people is that he is condoning its use.

"The line Scotland Against Drugs has taken follow those findings made by the House of Lords report in November of last year which was based on research done by world-renowned experts.

"They found that there was no reason for the current laws on cannabis to be changed."

Mr Ramsey added: "I would say the bishop's comments were ill-informed."