Cannabis for recreational use should be available in shops under similar restrictions to those used to control the sale of alcohol and tobacco, according to Britain's leading expert on the drug.

Under one scenario, people would be able to apply for a licence to buy cannabis products once they reach the age of 21, provided they have the approval of a doctor, he said.

The drug would be regulated by a body that ensures the quality and safety of the products before they go on sale.

A rethink of the laws surrounding cannabis and related products was necessary to take cannabis out of the hands of criminals, said Roger Pertwee, professor of neuropharmacology at Aberdeen University.

In the 1970s, Pertwee co-discovered THC, the active ingredient in cannabis.

Speaking ahead of a talk this week at the British Science Festival in Birmingham, Pertwee said: "In my view, we don't have an ideal solution yet to deal with recreational cannabis. We should consider licensing and marketing cannabis and cannabis products just as we do alcohol and tobacco.

"At the moment, cannabis is in the hands of criminals, and that's crazy. We're allowed to take alcohol, we're allowed to smoke cigarettes. Cannabis, if it's handled properly, is probably not going to be any more dangerous than that."

The government upgraded cannabis to a class B drug late last year against the advice of the Advisory Council on the Misuse of Drugs. The council's chairman, Professor David Nutt, was sacked after criticising the government's drugs policy, a move that prompted five others to resign in protest.

Possession of class B drugs, which include amphetamines, such as speed and barbiturates, carries a maximum penalty of five years in prison plus a fine. Dealing the drugs can lead to a 14-year prison sentence. The most recent Home Office figures show there are 158,000 convictions for cannabis possession a year.

Pertwee said he wanted to reopen the debate on cannabis, saying he favoured legalisation if the drug was well regulated. He added that healthier alternatives to smoking cannabis were available.

Outlawing the drug forced users to either grow it illicitly or buy it from an illegal dealer. "They have no idea what the composition is, what has been added to it, and they are at risk of being invited to take other drugs," he said.

Attempts to relax the ban on cannabis have been countered by concerns that it can cause schizophrenia in a minority of people who are susceptible to the condition. Pertwee said it might be possible for doctors to assess people's backgrounds and risk of mental health problems before allowing them to buy a cannabis licence.

"You would need a minimum age of 21, but I would go further: that you have to have a licence. You have to have a car licence, you have to have a dog licence; why not a cannabis licence, so you can only take it if it's medically safe for you to do so?" he said.

Nutt, who is a professor of neuropsychopharmacology at Imperial College London, said: "I welcome this attempt by the UK's leading expert on cannabis to bring rationality to the debate on its legal status.

"As cannabis is clearly less harmful than alcohol, criminalisation of people who prefer this drug is illogical and unjust. We need a new regulatory approach to cannabis. The Dutch coffee-shop model is one that has been proven to work but some of Professor Pertwee's new suggestions may well have extra benefits and should be actively debated."