Opposition politicians have expressed concern over newspaper allegations that illegal immigrants have been employed in several departments and agencies.

Reports in the Mail on Sunday suggested that 349 illegal staff have been employed, including a number of cleaners at the UK Border Agency’s (UKBA) central London headquarters.

The details were obtained by the paper through Freedom of Information requests.

Altogether, three government departments, 34 local authorities and 54 NHS Trusts admitted hiring illegal workers since 2006. Six were employed as teachers at secondary schools, while four became doctors, according to the newspaper.

Shadow home secretary Chris Grayling said the fact that UKBA - the Home Office agency responsible for vetting immigrants - had employed illegal staff was of particular concern.

"It suggests that the security in the Home Office is inadequate and that ministers are complacent about the issue," Grayling told the paper.

But a spokeswoman for the Home Office said: "The 12 illegal workers identified since 2006 were all sub-contractors, none of them were directly employed by the Home Office.”

"It was our checks and the strict regime we operate on illegal working in the UK that brought these cases to light.”