More than 11,000 illegal workers may have been cleared to get jobs as security guards in the latest Home Office gaffe, Home Secretary Jacqui Smith revealed yesterday.

The Security Industry Authority handed permits to 6,650 illegal workers, plus a further 4,450 people who immigration officials believe may not have the right to work in Britain.

It makes a total of 11,100 who should not have slipped through the net and won their licences to get jobs. But so far only 409 licences have been terminated.

Ms Smith told the Commons the SIA had written to 10,500 people who hold its licences informing them the authorisation may be withdrawn, but there was a "minimum 42-day period for that process to happen".

Initial estimates had put the figure at 5,000 and last month Ms Smith indicated it could be as high as 10,000.

Yesterday's disclosure means nearly one in three of the 40,000 applications to the SIA made by non-European Union nationals should not have been granted.

The scandal emerged five weeks ago and it was disclosed that one of the illegal workers had been responsible for overseeing then-Prime Minister Tony Blair's car while it was being repaired.

It was also disclosed 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, particularly for any past criminal activity. The checks allow successful applicants to work on pub and club doors, as well as in sensitive security posts.

Shadow Home Secretary David Davis demanded to know how the system had "gone so badly wrong" and said there had been a "huge policy failure" in the Home Office.

He said: "This update has shown just how staggeringly complacent the Home Office's response to this latest shambles has been.

"Not only have the number of cases increased from 5,000 to 10,000 to 11,000, but the Home Office was alerted to this problem nine months ago."

Liberal Democrat home affairs spokesman Nick Clegg 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 simply 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."

"In the long litany of scandals which have rocked the Home Office, this latest example of Keystone Cops incompetence truly takes the breath away."