A British company has been found liable for the first time for victims of modern slavery in a landmark high court judgment.

The judge, Justice Supperstone, found in favour of six Lithuanian men who were trafficked to the UK and brought a civil case claiming compensation for being severely exploited by the Kent-based gangmaster firm that employed them, DJ Houghton Chicken Catching Services.

The men were sent by the company, run by the British couple Darrell Houghton and Jacqueline Judge, to catch chickens on farms around the country. They worked frequently on farms producing eggs for the leading supplier to major supermarkets.

The judge ruled that the men were owed compensation for the firm’s failure to pay the agricultural minimum wage, for the charging of prohibited work-finding fees, for unlawfully withholding wages, and for depriving the workers of facilities to wash, rest, eat and drink.

The workers have described living and working in inhuman and degrading conditions. They say they were forced to work back-to-back eight-hour shifts for days at a time, and were denied sleep and toilet breaks, forcing them to urinate in bottles and defecate in carrier bags in their minibuses as they travelled between jobs.

They also alleged that their pay was repeatedly withheld, while Lithuanian supervisors working with the couple abused and assaulted them, intimidated them with fighting dogs and threatened them with instant eviction if they complained. The accommodation provided was dirty, overcrowded and unsafe and infested with bed bugs and fleas, they claimed.

Laurynas Kelpsa, one of the victims, said he was pleased with the judgment but still shocked by what had happened to him. “It means at last that some justice has happened. We’ve waited four years and it’s been really hard being forced to remember [the experience] all the time to prove they did wrong.”

The amount of compensation will be assessed at a future date but is expected to run to hundreds of thousands of pounds for unpaid wages alone. A claim for personal injury is still to be heard.

Ten other Lithuanian men who were employed by the couple over the same period in similar conditions have now also brought a claim.

A Guardian investigation in 2012 revealed that the trafficked Lithuanians were working in supply chains producing premium free range eggs for McDonald’s, Tesco, Asda, M&S and the Sainsbury’s Woodland brand. The farm sheds they cleared of chickens also produced eggs under the Freedom Food brand, and included some sites producing for Noble Foods, the company that owns the Happy Egg brand.

Noble Foods is the UK’s largest egg company and both the firm and its chairman, Peter Dean, have been major donors to the Conservative party. The company helicopter has occasionally been loaned to David Cameron for election campaigning.

Police raided houses controlled by Houghton and Judge in 2012 and freed several suspected victims of human trafficking.

The Gangmaster Licensing Authority described the company at the time as “the worst gangmaster ever” and revoked its licence. The Lithuanian men were taken into the care of the national referral mechanism for victims of human trafficking, but no criminal charges have been brought.

The couple blamed a Lithuanian supervisor, Edikas Mankevicius, who has since returned to Lithuania, for the situation, but in the high court on Friday, Supperstone ruled that he was integral to the business’s operation and the company could not therefore simply escape its responsibilities in this way.

The Lithuanians’ claims were brought in a civil case by the law firm Leigh Day and mark a significant breakthrough in attempts for victims of modern slavery to get justice.

Their lawyer at the firm, Shanta Martin, said: “This is the first time a British company has been found liable for victims of trafficking and it is going to make a world of difference to our clients. It should be seen as a warning shot to businesses that they need to make sure modern slavery is eradicated from their supply chains.”

The anti-slavery commissioner, Kevin Hyland, said: “It is a disgrace that any British employer in the 21st century would exploit their workers in such conditions. There is a dark irony that a business producing free range eggs did so using slave labour.

“This case shows that employers who exploit their workers can and should be pursued through the courts for lost earnings. And while it will not make up for the suffering, the decision of the court to award compensation will act as some form of justice.”