Care workers on overseas visas have suffered rape, sexual harassment and exploitation, an investigation has found.

The distressing incidents were found in the testimonies of almost 175 people working for around 80 care providers via the health and care worker visa gathered by the Bureau of Investigative Journalism (TBIJ) and Citizens Advice.

“We work on a lot of difficult issues at Citizens Advice, but this is one of the most heartbreaking because of our limited ability to help people find a way forward,” Kayley Hignell, its interim director of policy, said.

“Our investigation shows that there are potentially thousands of people trapped in a system which leaves them vulnerable to abuse and threats, powerless to complain, and often losing thousands of pounds. These people are skilled professionals who keep our healthcare services running yet … the best we can sometimes do is help them access a food bank.”

In one shocking incident a migrant worker from South Africa was repeatedly raped by her manager at a care home but felt unable to report him to the police for fear of losing her job and visa.

In another case, a Caribbean care worker was sexually harassed by her landlord in accommodation arranged by her employer who had sponsored her to work in the UK.

In addition, a live-in carer from Ghana told the investigation they had been threatened with dismissal and having her visa revoked after complaining to her manager about not having a day off after nearly four months.

Shadow care minister, Andrew Gwynne, said the shocking findings highlighted how the government had failed to fix the crisis in social care.

“It is vital that we ensure we have a system where exploitation of overseas workers is not tolerated, and steps must be put in place to stop those who perpetrate abuse,” he said.

A Home Office spokesperson told TBIJ: “We strongly condemn offering health and care worker visa holders employment under false pretences and will not tolerate illegal activity in the labour market.

“We are committed to stamping out exploitation of those working in the care sector and have announced providers in England will only be able to sponsor migrant workers if they are undertaking activities regulated by the Care Quality Commission.”

New regulations requiring overseas care workers to be registered with the CQC were introduced by the government on Monday.