Concern is rising about the growth of drug dealing via the internet, the BBC has learned.

An investigation by BBC Radio 5 Live has revealed that more than 1,000 web sites world-wide sell drugs.

Sites located abroad are selling drugs to Britain.

For instance, one supplier in Holland takes 400 orders a week for cannabis from the UK for people who take the drug for health reasons.

UK web sites also deal in drugs. One Shropshire business man buys cannabis from a web site based in Devon, pays by credit card and receives it in a brown envelope by post.

The government's anti-drugs co-ordinator, Keith Hellawell, is said to be aware of and concerned about the problem.

But the global nature of the internet makes it increasingly difficult to police.

Authorities have no jurisdiction over suppliers abroad, and UK sites for drug dealers can switch their site names at short notice to avoid detection.

Heavy drugs

Peter Hampton, founder of the Global Internet Monitoring Agency, an international web crime fighting agency, told BBC Radio 5 Live that drugs and the equipment to use them are becoming increasingly available.

While his organisation tries to police the web the best it can, he says he learns about most of the drug sites from ordinary citizens.

His agency receives about 1,500 complaints a day about a range of issues including drugs, pornography and hacking.

But he, too, notes the difficulty in catching the perpetrators.

"We are not aware of every criminal activity on the internet and we just don't have the resources to address every single one," he said.

"We are dealing with a community of 500 million people...and we have to prioritise our issues. If we feel a minor is involved in a drug issue or someone is being injured then we will address it immediately."