Britain illegally cut living allowance payments to modern slavery victims struggling to recover from their ordeals and must repay hundreds of pounds to each of those affected, the High Court has ruled.

More than 1,000 survivors will share about £1 million (RM5,45 million) in repayments, lawyers involved in the case said. The ruling is expected to affect government plans to roll out payment cuts to others recovering from slavery next year.

"We are really pleased with the judgment," Anna Sereni of campaign group Anti-Slavery International told the Thomson Reuters Foundation.

"It gives (victims) back their independence... It means that instead of having to worry about what food is going to go on their plate every week, they are going to be able to attend things like medical appointments and counselling sessions."

The Home Office said it accepts the court judgment, but declined to comment on whether it will appeal.

People who say they have been enslaved can get counselling, housing and a weekly subsistence payment during a recovery period under the government's National Referral Mechanism (NRM) - the scheme whereby victims are identified and given support.

Earlier this year, the government cut subsistence payments to asylum seekers being cared for under the scheme from £65 to £38 a week, in what campaigners said was "a gift" to exploiters.

Judge: The government acted unlawfully

The government acted "unlawfully" when it lowered the payments unilaterally, Justice Nicholas Mostyn said.

He also rejected suggestions that slavery victims' needs were comparable to those of asylum seekers who get the lower living allowance rate.

"The claimants and anyone else subjected to the cut are entitled to be repaid," he wrote.

Lawyers bringing the court challenge said the reduction in payments had left victims unable to meet their basic living needs and put them at risk of being exploited again.

"A back payment can't make up for the lost time and support, but we hope that at least now our client and others affected by these cuts can start to stabilise and rebuild their life again," said Nusrat Uddin, representing a woman identified only as K.

The Home Office last week announced extra funds for survivors affected by the cuts so they could travel to essential appointments. It was not clear if that extra funding would continue in the light of the court ruling.

At least 13,000 people across Britain are estimated by the government to be victims of forced labour, sexual exploitation and domestic servitude. But police say the true figure could be in the tens of thousands.

- Thomson Reuters Foundation