A probe undertaken by officials has revealed that as many as 3,400 hospital employees, hired by one of the nation's biggest medical contractors are illegal immigrants.

It has been reported by the UK Border Agency that about 8% of the cleaners, security guards and cooks sent to the NHS for employment purposes by ISS Mediclean were not suppose to be employed legally in the first place.

As many as 5 NHS contractors were audited with the company by immigration officers after it was made public last November that various illegal immigrants were being exploited at Surrey's Kingston Hospital.

It has been reported by the London School of Economics that anywhere between 400,000 to 600,000 illegal immigrants might currently be employed at various places across the country, mostly working with small businesses which manage to escape official regulations, like takeaways and corner shops.

In its defense, ISS Mediclean said, "We have been working with the UKBA 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 cooperation with UKBA, at local and regional levels".