The British government acknowledged yesterday that some illegal immigrants had been employed as security guards, but said checks were underway to revoke their licenses and deport them.

Up to 5,000 illegal immigrants have been able to secure security jobs in the UK, including guarding the prime minister's car, the Sunday Mirror newspaper reported. Six illegal immigrants were found to be working for the Metropolitan Police, while others were employed at airports, ports and government buildings, the paper added.

The Home Office said that since 2004 it has been the job of the Security Industry Authority (SIA) to regulate the industry.

Established in 2003, it is an independent body reporting to the Home Secretary, which is responsible for granting licences to security staff including bouncers and private guards. The SIA took immediate action as soon as it became aware that some licence-holders had been employed illegally, the Home Office said. From July this year, all new applicants have been granted a licence only if they are entitled to work in Britain.

"Ministers ordered checks on all existing licence-holders and these will be completed shortly," the Home Office said in a statement. "Any individual found to be working illegally will have their licence removed and face removal from the UK."

The SIA was not immediately available for comment.

Nick Clegg, the Liberal Democrats spokesman on home affairs and party leadership candidate, said: "Public confidence in the government's handling of immigration will take yet another hammering with this revelation."