Hundreds of illegal immigrants have been working for the British Government in some of the country's most sensitive offices.
Some 349 illegal foreign staff have been given jobs with Whitehall departments, councils and NHS Trusts over the past four years.
The details were obtained by London's Mail on Sunday by putting in requests under the Freedom of Information Act.
The Home Office admitted employing a dozen illegal workers, 11 Nigerians and a Ghanaian. Ten of them were cleaners at Beckett House, the headquarters of the UK Border Agency, which is responsible for vetting immigrants.
The two others worked as a chef and a security guard at the Home Office itself - regarded as among the country's most likely terrorist targets.
Altogether, three Government departments, 34 local authorities and 54 NHS Trusts admitted hiring a total of 249 illegal 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 most worrying thing about this is that the Home Office clearly carried on employing illegal immigrants despite being warned two years ago that there was a problem.
"It suggests that the security in the Home Office is inadequate and that Ministers are complacent about the issue."
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."