Tesco is facing a UK lawsuit brought by Burmese migrants in Thailand, who claim that one of the supermarket giant's former clothing suppliers used their forced labour, lawyers said on Monday.

"Burmese migrants were made to work up to 99 hours a week on unlawful wages and in forced labour conditions at a Thailand factory making clothes for Tesco's F&F fashion range," said law firm Leigh Day, which represents the 130 claimants.

The claimants are demanding compensation from Tesco and its Thai subsidiary at the time, Ek-Chai, which it sold in 2020.

They accuse the companies of being "unjustly enriched at the expense of the adult workers".

The suit will also target Intertek, the insurance and auditing group which inspected the factory where the alleged forced labour took place.

If a settlement is not reached, the case will be pursued in the High Court in London, the legal firm warned in a statement.

The workers were employed in the VK Garments factory in Mae Sot, northwest Thailand, between 2017 and 2020, where they cut, made and packed garments to be sold in Thailand.

They were paid a maximum of £4.00 per day, and claim they were worked at a relentless pace for seven days a week and lived in tiny dormitories where they slept on a concrete floor.

Tesco said in a statement Monday that the claims were "incredibly serious" and that if it had "identified issues like this at the time they took place, we would have ended our relationship with this supplier immediately".

While Tesco was not involved in the day-to-day running of the factory, it said "we would continue to urge" its former supplier "to reimburse employees for any wages they're owed".

Compensation has so far only been awarded by the Thai courts, and only for severance pay. (AFP)