A ruthless gang led by a thug nicknamed "Little Frog" were yesterday convicted of plotting a terrifying extortion racket against Polish workers in Hereford.

The jury at Worcester Crown Court convicted four men of conspiring to commit blackmail at the end of a six-week trial.

Cash demands of up to £400 were made to victims in return for fixing up jobs at the Sun Valley poultry firm and other companies.

Threats were issued to enforce payment of the so-called "tax" and violence dished out to some of those who refused.

The thugs, who all settled in Hereford after emigrating from Poland, turned on their compatriots in a city they saw as "their town" to control, one witness told police.

Two men who upset the gang ended up in hospital with a broken jaw and a fractured eye socket.

Others fled from their Hereford homes in panic, some returning to Poland early and ditching five year plans to work in England.

Many of the vulnerable people targeted kept silent about the scam through fear of retribution and a lack of confidence in police in a strange country.

But Operation Tropical, launched by West Mercia Police, painstakingly built a climate for a change of attitude and provided protection for witnesses.

Working with interpreters and officers from Poland - sent to Hereford for six weeks to help the inquiry - detectives made major breakthroughs, interviewing over 200 Polish people.

The £1 million investigation is now being held up as a model for other forces to follow, providing guidelines on how to deal with gangs of east european criminals in the UK.

Det Sgt Martin Barnes, of Hereford Police, said: "The gang thought they could get away with it and often operated in broad daylight. They didn't think their victims would help the police.

"I have never worked on an inquiry where there existed such a climate of fear. We needed to gain the trust of victims, which we did. Now Polish people in Hereford are once again free to walk about in safety."

Judge John Cavell paid tribute to the work of the police in a difficult case and said: "I want to record the public's appreciation. The Polish community owe them a debt of gratitude for their efforts."

Convicted of the conspiracy between March and December 2007 were: Krzysztof Wojcik, 29, of Marlowe Drive; Jaroslaw Wysiecki, 23, of Grenfell Road; Michal Zubrzycki, 20, of Ledbury Road; Kamil Siegien, 30, of Coningsby Street.

Zubrzycki was also found guilty of causing grievous bodily harm with intent to Marcin Walus but cleared of the same offence against Robert Szymczak on the directions of Judge John Cavell.

Wojcik, the gang's 21-stone ringleader called Zaba in Polish - or "Little Frog" - laughed contemptuously as they were led to the cells.

He had served sentences totallig nine and a half years in Poland for robbery and fraud.

But under EEC rules, he was free to travel to the UK and live here. Only those who pose a threat to state security are banned.

Siegien, who was caught in Scotland after trying to escape the police net, had a record for assault, Zubrzycki for drugs and Wysiecki for theft.

The gang will be sentenced next month along with a fifth man who pleaded guilty to assisting an offender before the trial began. He is also in custody.

Grandmother Jolanta Witczak, 41, of Kingsway, Hereford, was cleared of witness intimidation after over eight hours of deliberation by the jury.