In April he was among the prominent people who put their name to the Australia21 report that declared the "war on drugs" a failure and called for renewed debate on ending prohibition.

He said in an interview this week he had long been in favour of changing drug laws, so it had been ''to an extent frustrating to see the law applied'' when he was DPP. But his views had been ''irrelevant to the conduct of the office''. Changing the drug laws would be a "huge undertaking" which would take a long time because the case for change had to come ''from the electorate to the politicians", Mr Cowdery said.

A strict system of licensing for the manufacture and distribution of drugs including marijuana, cocaine and ecstasy would be needed. ''Licences would be very difficult to get and very easy to lose and would need to be policed," Mr Cowdery said. State-supplied drugs would be cheaper, he said, because the risk associated with illegality dramatically inflated the price.

Pricing was a policy matter but tax revenue from drug sales could be used to fund rehabilitation programs for addicts. Mr Cowdery stressed that different drugs should be treated according to their associated harm.

The head of policy research at the National Drug and Alcohol Research Centre at the University of NSW, Alison Ritter, said no country had implemented full legalisation. The concern was that drug use might increase and, given patterns of alcohol and tobacco consumption, that concern appeared justified, she said.