An EU agency has highlighted the heightened risk of foreign domestic workers in the UK enduring slavery-like conditions but conceded its pan-European study of labour conditions had been impeded by “mafia networks”.

The study (pdf) by the EU Agency for Fundamental Rights (FRA) found exploitative employers had a feeling of impunity across Europe but that legislative gaps in Britain were raised as one of its particular concerns.

The report noted that in the UK, Belgium, Greece, Luxembourg and Sweden domestic workers were excluded from legislation capping the number of hours an employer can ask them to work.

It also raised the issue of visas for domestic workers from third countries being tied to a specific employer, leaving “domestic workers to endure exploitative working conditions in order to keep the job which allows them to legally reside in the country of work”.

Campaigners have long warned that thousands of foreign domestic workers are being enslaved behind closed doors in some of Britain’s wealthiest neighbourhoods, often by families from the Gulf.

All but two of the 10 domestic workers interviewed in the UK by the FRA had been brought to the country by their employer from the Middle East.

The UK changed the law in 2016 to allow overseas domestic workers to switch employers within the six-month term of their visa. But critics say employees do not know their rights and are not in a position to look for new work.

According to interviews conducted by the agency’s researchers, one Filipino maid working in the UK was denied food by her employer and relied on biscuits taken from hotels and eating the children’s leftovers, the report said.

“Undernutrition was a main reason for escaping employers, as workers could no longer survive without food,” the report said of the plight of the domestic workers interviewed in the UK.

A second maid from sub-Saharan Africa said of her experience at the hands of her employer in Britain: “I hoover. He took that hoover and beat me in the hand. Then I scream and I scream, and the small boy came: ‘Auntie, what is the problem? Are you beating her, daddy? They tell us in school that you are not supposed to beat ladies. Why are you beating auntie?’”

The report, covering a range of employment from fruit picking to kitchen work and construction, published interviews with 237 adult workers who have been victims of severe labour exploitation between 2013 and 2017, but reported difficulties in gaining access in France where researchers were “confronted with mafia networks”.

One Polish man said of his life in the UK: “It’s very difficult for me to express and for you to understand the living conditions we were put through. The accommodation and even the place where we were taking a bath, you know the hens were treated better.

“There was no bathroom in the caravan, we had to go about 10 metres to the garage, there was a bathroom there and it’s winter. There was only a bath[tub] there and in the middle of winter you are sitting there having a bath and you blow and you can see the air coming out of your mouth. […] It was just unimaginable.”

Michael O’Flaherty, the FRA’s director, said he hoped the new EU labour authority due to begin work later this year coordinating the member states could help people trapped in servitude.

He said: “We need to do a much better job of regulating domestic labour. It’s too easy to get away with unacceptable behaviour … When the labour is at home, hidden behind the front door of private residences.”

Bulgarian authorities announced on Tuesday that they had broken up a major organised crime ring thought to have smuggled thousands of migrants, predominantly boys aged under 16, from Afghanistan en route to western Europe. They said the gang had been active since early 2017, making weekly transfers of 30 to 40 people at a time.