Prime Minister David Cameron rejects the idea of a royal commission on the UK's drug policy suggested by the Commons home affairs select committee. Press Association

David Cameron has ruled out a royal commission to consider the decriminalisation and legalisation of illegal drugs on the grounds that the government's current approach is working.

A report by the Commons home affairs select committee said that after taking evidence from all sides of the drug debate, "now, more than ever" there is a case for a fundamental review of all UK drug policy.

The influential cross-party group of MPs said the prime minister should urgently set up a royal commission to consider all of the alternatives to Britain's current drug laws, including decriminalisation and legalisation.

The committee chair, Keith Vaz, told the BBC Radio 4 Today programme that a royal commission to look at every aspect of drugs policy and report back by 2015 is "not a big ask".

But Cameron said he wanted the focus to be on policies that were working rather than a long-winded royal commission.

"I don't support decriminalisation. We have a policy which actually is working in Britain. Drugs use is coming down, the emphasis on treatment is absolutely right, and we need to continue with that to make sure we can really make a difference. Also, we need to do more to keep drugs out of our prisons.

"These are the government's priorities and I think we should continue with that rather than have some very, very long-term royal commission."

Among the recommendations contained in a report published on Monday, Drugs: Breaking the Cycle, the MPs say Home Office and health ministers should be sent to Portugal to examine its system of replacing criminal penalties for drug use with a new emphasis on treatment. They say the Portuguese example clearly reduced public concern about drug use and was backed by all political parties and the police.

The MPs also suggest the British government should fund a detailed research project monitoring the recent legalisation of marijuana in the US states of Washington and Colorado and the proposed state monopoly of cannabis production and sale in Uruguay.

The Liberal Democrat home office minister Jeremy Browne insisted the government was making good progress on drugs but said it was "open to imaginative thinking" on drugs policy.

"We are open-minded, we think it's a decent, thoughtful, balanced report," he told the BBC Radio 4 Today programme. "We will consider it carefully.

"The home secretary has said that she doesn't think that a royal commission is the answer at this time but we are open to new ideas and evidence-based research to carry on reducing the harm caused by drugs in this country."

On the government's current strategy, he said: "It is not true to say we are making no progress on drugs. There's been … dramatic falls in the amount of drugs consumption happening and the harm caused by drugs.

"That includes very serious drugs so heroin, for example, crack cocaine, there have been dramatic falls in recent years. The average age of heroin addicts is going up. Fewer younger people are coming on stream as heroin addicts. There's been significant progress on treatment."