'Foreign gangsters behind most of organised crime in UK'

Bill Hughes, director-general of the Serious Organised Crime Agency, said gun crime, drugs and people smuggling are heavily linked to overseas gangsters.

He told MPs on Tuesday: "Most of the crimes we are dealing with are international. The source of the trouble starts elsewhere."

His comments came as Sir Stephen Lander, SOCA's chairman, warned that large-scale "cannabis factories" run by Vietnamese and Chinese criminals are springing up across the country.

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Hidden in ordinary houses, the factories are producing huge quantities of high- strength skunk cannabis on an "industrial scale".

Sir Stephen told the Commons Home Affairs Select Committee: "There are wide areas of the country where this is being grown commercially.

"It's not as though people are growing it in a couple of pots on their window sills."

Sir Stephen also expressed concern about the growing number of migrants from outside the EU seeking to exploit lax European border controls to enter Britain.

He revealed that new visa requirements for all South African visitors could be introduced because thousands of illegal immigrants are using the country as a gateway to the UK.

Ministers are to look into current rules whereby all South African passport holders can enter Britain without a visa, after SOCA helped to expose the huge scale of organised document fraud.

Last week, it was revealed at least 6,000 illegal immigrants - mostly poor Indian workers - had been smuggled into the UK via South Africa.

The villagers, who were charged up to £30,000 a time, were given genuine passports which were obtained fraudulently from corrupt officials.

Sir Stephen told MPs that identifying the connection represented an early success for his agency, which was set up in 2006 to tackle the criminal gangs' "Mr Bigs".

Although he admitted SOCA had struggled in its early months to understand patterns of people-trafficking gangs and organised illegal immigration, he insisted it is now having "some success".

Sir Stephen also faced tough questioning over whether the agency is providing value for money for its £440million annual budget.

SOCA has been attacked in recent months over its apparent failure to stem the flood of drugs coming into the UK.

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But he insisted that operations overseas - including successful seizures at sea by the Royal Navy - are starting to have an impact.

He claimed cocaine wholesale prices are £5,000 greater in the UK than in the Netherlands, pointing to a radical reduction in the supply of the drug.

However, he did admit that this had made little difference to street prices and that, increasingly, the drug was being diluted or "cut" with other substances before being sold cheaply on the streets.

During the session, Labour MP David Winnick asked him: "There doesn't seem to be the slightest indication that organised crime in this country is being undermined.

"Master criminals are not going in fear of their lives because of your organisation. Why should the British public consider that you have made the slightest difference?" But Sir Stephen insisted the pay-off from SOCA's new approach would come "in two or three years' time", adding: "We've been going 21 months.

"This is a marathon, not a sprint. We need some time and space to get on with it."

Last night, Home Office immigration minister Liam Byrne said no final decision had been made over whether to force South African visitors to apply for visas.