Two Latvian men have been found guilty of acting as illegal gangmasters, supplying Latvian and Lithuanian workers from the Wisbech area to pick leeks, cabbages, broccoli and flowers, for supermarket supply chains across East Anglia.

Juris Valujevs, 36, and Ivars Mezals, 28, were convicted at Blackfriars crown court, London, of operating without a gangmaster’s licence after a nine-week trial in which the court heard evidence about exploitation, control by debt-bondage, overcrowded housing, and allegations of sham marriages arranged to facilitate illegal immigration.

The two men, together with Valujevs’ wife, Oksana Valujeva, 33, and their close Latvian friend Lauma Vankova, 26, were also charged with conspiring to arrange sham marriages to enable non-EU men to breach UK immigration laws. Mezals was found not guilty on this charge but the jury failed to reach a verdict on it in the case of the other three after a week’s deliberation, and were discharged. The crown is considering an application for a retrial on the sham marriage charges.

The jury of seven women and four men had been directed earlier by the judge, David Richardson, to clear the two men of a further charge of fraud relating to excessive rent.

The case has laid bare a tough, often squalid, world in which the two men were able to operate outside the law for more than four years.

A succession of workers from eastern Europe described a precarious existence in the fens. They got up at 4am to be taken to distant fields where they endured hard labour outside, on the minimum wage, often on 12-hour to 14-hour shifts, or to polytunnels and packhouses, where they prepared vegetables and flowers for supermarket orders.

They described a system of erratic employment in which their hours were never certain and might only be confirmed the evening before in a text from one of the two men.

Most lived in sub-let rooms in modest housing in Wisbech, paying £50-£60 a week to one of the two Latvians for a room that might be shared with two or three others. One of the smaller properties at one point housed 11 adults.

Both Mezals and Valujevs had themselves started out working the fields on the minimum wage when they arrived in the UK from Latvia, Valujevs coming in 2003 and Mezals about 2006.

The pair went on to run various business, from trading in scrap cars that they fixed and operating cars and minibuses for taking migrants to work, to letting property, collecting clothes door to door to send to eastern Europe for a charity registered in the British Virgin Islands, and shuttling luggage the UK and Latvia for other migrants.

The court heard the two men were unlicensed gangmasters, supplying Lithuanian and Latvian workers to other gangmasters, who in turn sent them to the agricultural and packing work. They promised Latvians willing to come to the UK to work regular well-paid jobs and good accommodation but then put them in to overcrowded and dilapidated houses, some of which were infested with bed bugs.

Work was withheld, the prosecution said, until tenants became indebted to the pair; that debt was used as a means of controlling them. The victims suffered threats and intimidation.

Mezals sometimes collected the workers’ pay himself or had it paid into his personal bank accounts, or in other cases waited for workers in his minibus to take rent and purported debts from them as soon as they were paid. Witnesses said deductions were sometimes made arbitrarily, so that they often ended up with only £20 for a full week’s work.

Two witnesses told the court that they were threatened that, if they complained, they might end up “like Alise”, a young Latvia woman who had gone missing and been found dead on the Sandringham estate.

According to the prosecution, the control over some of the women took a more sinister form. Mezals and Valujevs controlled the amount of work they were given so that they never fully paid off what they owed. Then once they were heavily indebted they were pressured to pay off those debts by entering sham marriages to Asian men.

All four defendants denied being part of any conspiracy involving sham marriages. Mezals was found not guilty on this charge and the jury failed to reach a verdict on it for the other three defendants.

Counsel for the defence highlighted inconsistencies in the evidence from the prosecution witnesses and said all the women making the allegations relating to the conspiracy charge had a motive to lie: they had either committed an offence of sham marriage and wished to avoid prosecution themselves so cooked up a story to implicate the others, or were making the allegations so they could present themselves as victims in need of housing and benefits.

The defence, supported by several witnesses, argued that the Latvian men had not been acting as gangmasters but simply helping others of the tight-knit eastern European community find housing and work with other gangmaster companies.

They pointed out that among the prosecution witnesses were self-confessed alcoholics who had been sleeping rough behind Wisbech’s Tesco superstore and washing in its toilets until put in touch with Mezals and Valujevs who had helped them with housing and jobs.

But Valujevs had previously applied for and been refused a gangmaster’s licence himself and the jury agreed with the prosecution that the two men were partners supplying workers to other businesses illegally.

Valujevs has previous convictions for theft and traffic offences in Latvia and convictions in the UK for drink driving, for obstructing the police, and driving while disqualified and without insurance. Mezals, a qualified car mechanic, has a previous UK drink driving conviction.

Sentencing is expected to take place on Friday.