Nearly 1,000 illegal immigrants have been employed at one of the country's largest NHS private contractors, it has emerged.
An audit by the UK Border Agency of a few health service contracts with ISS Mediclean in the south-east of England found that 8% of its workers were illegally working as cleaners, catering staff and security in hospitals.
The results, reported by Channel 4 News, follow a report by the broadcaster last year on ISS staff at Kingston hospital, which also found the NHS trust hired illegal immigrants.
Immigration officers found that 8% of the 1,500 staff employed in cleaning, catering and security were working without the right to remain in the UK. ISS said it employs 10,000 similar workers within the M25, meaning if the findings were repeated across the board, there would be about 1,000 illegal workers.
However, ISS has carried out all the required checks including passports and national insurance numbers, which the UK Border Agency accepts as defence of due diligience.
ISS said: "We have been working with the UK Border Agency to define best practice in avoiding the hiring of workers without the required genuine paperwork.
"We have looked at a number of areas and enhanced our processes accordingly and have made recommendations on how to further improve co-operation with UK Border Agency, at local and regional levels."
Phil Woolas, immigration minister, said: "Last year there were 64,000 removals from this country, so I don't accept the report at all. It's painting one side of the picture."