The number of migrants found to be illegally working in the private security industry is more than double the figure given by the Home Office last month.

More than 11,000 migrants were issued with the licences by the organisation set up to vet those employed as security guards and doormen, despite having no right to work in this country.

The latest figures show that an estimated one in four of 40,000 nonEuropean foreigners issued with licences by the Security Industry Authority (SIA) had no right to work in Britain – the first large-scale view of the extent of illegal working in low-paid jobs.

Jacqui Smith, the Home Secretary, told MPs yesterday that more than 6,600 immigrants had been given licences to work, 1,600 more than the estimate given to MPs last month. She said that the SIA had issued permits to a further 4,400 people who immigration officials now believe may not be entitled to work.

Initial estimates had put the figure at 5,000 but the figure has mounted as the SIA carried out a review of about 40,000 licences issued and checked the names against a database held by the Border and Immigration Agency.

Despite the admission that thousands of immigrants have been given licences, only 409 licences have been revoked. The SIA said that it took a minimum of 42 days to revoke a licence as those issued with the document had a right of appeal.

Ms Smith told MPs that the authority had written to more than 10,000 people telling them that their authorisation could be withdrawn. She said that the Border and Immigration Agency had started investigations into 328 of those referred to it, carried out 101 enforcement visits and arrested 15 people. By the end of January they planned at least 400 further visits.

The scandal emerged five weeks ago and it was disclosed that one of the illegal workers had been responsible for Tony Blair’s car while it was being repaired. Mr Blair was Prime Minister at the time. It was also disclosed that Ms Smith had accepted Home Office press office advice in August not to tell the public about the mistakes.

The SIA was set up by Labour to vet doormen and security personnel, with the intention of screening out those with a criminal record. The checks allow successful applicants to work on pub and club doors, as well as in sensitive security posts. Officials in the Home Office were first alerted to a possible problem in April, and in July the checks on everyone who had been issued with a licence began.

The Security Industry Authority has admitted that a form given to those seeking a licence does not contain a question asking them if they have the right to work in the United Kingdom.

It was only in July that processes were introduced under which information on applicants is sent to the Border and Immigration Agency for it to check against databases that show who has the right to work. Until the beginning of October a foreigner could be given a licence without necessarily producing a passport.

Nick Clegg, Liberal Democrat home affairs spokesman, said: “We now know that over one in four employees may be working illegally, and that the most basic checks on their right to work were not taking place. Worse still, the Government appears to have been extremely slow in recognising the problem and slower still in coming clean about the sheer scale of it.”

Mr Clegg added: “Is it any coincidence that this statement has been smuggled out on the same day as 24 government statements, Gordon Brown’s appearance before the Liaison Committee and the signing of a new EU treaty?”

David Davis, the Shadow Home Secretary, demanded to know how the system had “gone so badly wrong” and said that there had been a “huge policy failure” at the Home Office.

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