Three managers at a cleaning company in a London hospital have been arrested on suspicion of blackmailing illegal migrant workers.
The managers at private firm ISS Mediclean, aged 47, 43 and 28, were arrested on Thursday during a raid at Kingston Hospital, south-west London.
Foreign employees without the right to work had allegedly been warned they would be reported to the authorities.
The company employs 43,000 staff at hospitals across Britain.
UK Border Agency officers were present when the company's office in Kingston Hospital was raided.
An ISS spokesman said: "ISS deeply regrets any adverse reaction this incident may have had on the patients, staff and visitors to the hospital.
"It is our responsibility to work within the law and to ensure that our employees do the same, which includes demonstrating their right to work legally."
He continued: "Immediate steps have been taken to ensure the correct levels of management and staff remain in place."
It is believed the initial tip-off was supplied by Kingston Race and Equalities Council.
A Kingston Hospital spokeswoman said: "The trust is grateful to the police and the UK Border Agency for the attention they have given to this issue.
"This is now a police matter and so we are unable to make any further comment."