By Liz Carney BBC Radio 4's File on Four

As many as 2,000 workers are working in Kings Lynn

As the UK's illegal labour market grows out of control, a BBC investigation reveals the methods used by Chinese gangsters to traffick labourers from rural China to Britain.

On East Anglia's vegetable fields, thousands of casual workers are needed to cope with the endless cycle of picking and packing.

Most work long hours for little pay. Increasingly found amongst them are the thousands of Chinese migrants now being trafficked into the UK by violent "Snakehead" gangs.

As many as 2,000 of these illegal workers are already thought to be living, sometimes 20 to a house, in Kings Lynn. One man gave us a rare insight into the how the multi million pound human smuggling operation works.

Travel debts

He was too frightened to be identified.

"I had to pay a Snakehead �20,000 to get to England. I flew to Europe and came to England on the train through the tunnel and on the train I tore up my documents."

Once in Britain the man was told to call contacts who sent him on to Kings Lynn.

David Black, an authority on Chinese gangs, says the immigrants become reliant on a sophisticated network.

"They'll be passed from house to house. They'll come off the boat or however they arrive and then be told they have to work in order to pay off their travel fee.

"Basically, they're entering slavery."

Fatal consequences

Concern grew recently when officers from the Metropolitan Police serious crime group travelled to Kings Lynn to investigate the death of a man shot in a crowded bar in London's China Town.

It is believed he may have been the victim of a turf war between Chinese Triad gangs. Snakeheads were behind the death from suffocation of 58 Chinese people in a lorry in Dover.

Up to 20 Chinese immigrants live in one house

For those who do make it, failure to pay their travel debts can have fatal consequences to themselves or their families back home in China.

This means they must find work fast, and to do that they must break the law.

The Chinese worker in our programme told us: "The agencies do ask for papers but my friends photocopy documents to prove they can work - they are not genuine papers.

"Some they have to pay for, some they have to make on the computer. The recruitment agencies know these papers are not quite right."

Of course there is an illegality, of course there is abuse, of course the mafias are getting involved in this sector David Curry, Chairman, Select committee on the environment, food and rural affairs

The immigrants earn as little as �2 an hour.

Henry Bellingham, the local MP, has had confidential briefings on the situation and says those who make use of the labour must share the blame.

"These Chinese people have arrived in Kings Lynn because the whole framework of the people trafficking organisation knows that in Kings Lynn you've got accomodation and jobs available so it's obviously a vulnerable target.

Report due

"There are factories in West Yorkshire and Cambridgeshire where there are growers who historically have not asked questions.

"They have asked for a certain amount of labour on a certain day. These farmers have turned a blind eye - they know only too well what's going on."

Mr Bellingham's concerns are shared by the chairman of the Commons Environment, Food and Rural Affairs Committee.

It is due to publish a report into the efforts of various government departments to bring gang masters acting illegally into line.

'Police matter'

Its chairman, David Curry, believes a failure to tackle the gang masters is opening the door to organised crime.

"Of course there is an illegality, of course there is abuse, of course the mafias are getting involved in this sector.

"It's an easy sector in which to operate because they are not being chased hard enough and there doesn't seem to be the political will to crack it."

The Minister for Food and Farming, Lord Whitty, denies that the government is not doing enough and says serious criminality is ultimately a matter for the police.

File On 4: BBC Radio 4 on 22 July at 2000 BST and on 27 July at 1700 BST