Tony Blair has been asked why anyone should have faith in the government's drug policy following the resignation of Keith Hellawell.

In the Commons, Iain Duncan Smith called on the prime minister to say whether the public should choose between the home secretary's views and the views of Blair's own "drugs tsar".

"Why should anyone now have confidence in the government's drug policy when the prime minister's own drugs tsar has resigned saying it is all wrong," he asked.

Blair conceded that there were "differences of view" on the issue of reclassifying cannabis.

But he called on the Conservative leader to "debate the actual policy itself rather than scoring points" on the drugs issue.

He said it would be "absurd to say that everyone was of the same view" on the cannabis question.

"The change that will be proposed by the home secretary is a change supported by the Advisory Council on Drug Misuse, which includes many senior police officers, by the home affairs select committee, which includes many Conservative MPs, by the Association of Chief Police Officers, which is the association chief constables and also by the Metropolitan police," the prime minister said.

Duncan Smith said that the government was sending the message to young people that it was "OK to get stoned".

The Tory leader said that the prime minister argued that Hellawell had a "formidable record in tackling drugs".

He demanded to know what had changed since then.

Whilst the prime minister praised the "extremely important" work carried out by the drugs tsar, he refused back his criticism of moves to soften the laws on cannabis.

He insisted that the possession of cannabis "remains a criminal offence" but would free up the police to focus on hard drugs and dealers themselves.

But Duncan Smith said the government was basing the change on the failed drugs policy piloted in the south London.

The Tory leader said the Lambeth project had sent out the message that drug use was acceptable.

"If he was the parent of a 16-year-old living on that estate would he want that kind of a message going out to those children?" he asked.

The prime minister refused to be drawn on the issue - insisting that the Lambeth project had increased the number of drug arrests and reduced street crime.