DRUG cartels and suppliers are increasingly using the postal system to smuggle their narcotics into Britain, according to investigators.

Gangs are circumventing tighter Customs checks at traditional ports of entry by transporting heroin, cocaine and ecstasy by post, which is less effectively screened.

There has also been a growth in illegal internet pharmacies in Southeast Asian countries such as Thailand that sell and post restricted medicines, including the sedative diazepam.

Once delivered in Britain, they are consumed as recreational drugs.

The growth in the trade has prompted calls by drugs experts for tougher penalties and more resources to be devoted to postal screening.

Although Customs attempts to screen all letters and packages entering Britain, some of its biggest successes have been achieved by prior intelligence.

The problem is expected to be highlighted in a report next month by the United Nations International Narcotics Control Board, which, it is understood, will warn that medicines are in high demand among drug addicts.

One of the biggest recent medicine seizures — from Thailand — was a postal consignment of clonazepam, normally used to control bodily seizures and anxiety.

Drugscope, which monitors drug abuse in Britain, said the scale of drug-selling through internet pharmacies was still under-researched but was potentially huge.

A spokeswoman said: “Anyone with an e-mail account will know how many of these drugs get advertised through spam e-mail. Most of these spam e-mails you get sent are about drugs.”

Some illegal internet pharmacies are also producing drugs such as ecstasy, which they then sell on to drugs cartels.

One of the biggest consignments of drugs by mail found was more than 16,000 ecstasy tablets seized in 2004. The investigation involved Australia, Canada, New Zealand, Thailand and Turkey.

Cocaine abuse in Europe is also increasing, according to the UN. In the UK, the British Crime Survey estimates that almost 5% of 16 to 24-year-olds have taken the drug in the past year, although usage dropped in older age groups.

According to the National Criminal Intelligence Service, between 35-45 tons of cocaine, with a potential street value of £3.5 billion-£4.5 billion, enter Britain each year.

The profits to be made are highlighted by the so-called “Bling Bling” gang, a mob of crack cocaine dealers. Police believe they imported about £48m worth of the drug into Britain over two years, though they fear the actual amount could be much higher. At their peak, the gang were bringing in up to £3m worth a week.

The cartel — which had about 50 members — operated from London, Paris and New York, and usually imported drugs from the Caribbean into Europe using human “mules” on passenger jets.

Police have described it as one of the most significant international drugs gangs of its kind. This week, 14 of its members will appear before Snaresbrook Crown Court for sentencing. A further 25 people have been convicted in France, and 10 in the United States.

According to UN investigators, most of the cocaine entering Britain comes from South America, usually via a new route through west Africa and mainland Europe.

Consumption of heroin in western Europe is said to have stabilised and may even be declining in some areas of Britain, partly because of the growing fashion for other drugs such as cocaine. Most of the heroin trade in Britain is controlled by Turkish gangs based in northeast London.

Cannabis remains the most popular and widely abused drug in Europe. Last year, about 30m people are estimated to have taken it across the continent. About 15% of 15-year-olds in the European Union smoke it more than 40 times a year.

Britain remains one of the highest consumers of cannabis in Europe, along with other drugs including cocaine and heroin. Experts cite various causes, including Britons’ “binge” mentality.

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