Ruslan Kulish and his girlfriend will be sentenced next month

The "gangmasters", who all lived in Cambridgeshire, were convicted at King's Lynn Crown Court in Norfolk.

The convictions centre around Ultimate Source, a seasonal labour firm set up to supply Eastern European workers to farms and factories in the UK.

It is alleged the gangmasters earned about �4m bringing in foreign workers and owe more than �1m in tax.

We hope the successful conclusion of this investigation will send a warning to anyone engaged in these kind of illegal activities Detective Constable Kim Bowen Cambridgeshire How the racket worked

Briton David Mutch, 58, of Soham and Ukranian national Ruslan Kulish, 27, of Ely, were convicted of possessing false documents and transferring criminal proceeds.

John Carter, 58, of Caldecote, was also convicted of concealing or transferring the proceeds of criminal conduct.

Latvian Veronika Linzuza, 27, who also lives in Ely, Ukrainian Viktoriya Kulish, 24, who is Ruslan Kulish's sister and Ukrainian Denis Lyashkov, 27, of Littleport, were also convicted of concealing or transferring the proceeds of criminal conduct.

Viktoriya Kulish admitted deception and Denis Lyashkov was also convicted of deception.

Ruslan Kulish was also convicted of possessing replica immigration stamps,

Mutch and Carter are free on bail and the other four are being held in custody until they are sentenced on 2 April.

Unpaid tax

Carter, Mutch and Ruslan Kulish set up Ultimate Source in 2000.

Farmers testifying in the case told the court they believed the workers they had hired through the company were brought in to the country with legal papers.

Lyashkov and his girlfriend Viktoriya Kulish laundered money for the gang

They said they had been told income tax and national insurance would be taken care of by the company.

It is thought Ultimate Source brought in about �4m and failed to pay hundreds of thousands of pounds in taxes owed to the government.

The firm supplied labour to farms in areas throughout the UK, including Cornwall, Inverness, Hertfordshire, Essex, Herefordshire, Oxford, Norfolk, Lincolnshire, Cambridgeshire and Bedfordshire.

The group were charged following a joint investigation between Cambridgeshire Police and the Immigration Service.

Detective Constable Kim Bowen, one of the officers at the centre of the investigation, said: "It's a fantastic result because it's involved a lot of hard work for everybody in the team since last April.

"The issue of gangmasters is very topical since the tragedy at Morecambe and we hope the successful conclusion of this investigation will send a warning to anyone engaged in these kind of illegal activities."

Those from eastern Europe face deportation after serving their sentences. Police said all four had overstayed their visas.