The authority licenses bouncers, bodyguards and shop security guards
The chief executive of the government body which licenses bouncers and other security workers has resigned.
Mike Wilson, head of the Security Industry Authority, stepped down after it emerged that some of its own agency staff had not been security cleared.
Last year, it emerged that the SIA had wrongly given licences to more than 6,600 illegal immigrants.
The government said there had been "some failings". The Tories called the government "staggeringly complacent".
Home Office minister Alan Campbell said plans were being made to replace Mr Wilson following "some failings" in the SIA's compliance with security clearance requirements.
He said that 38 temporary workers hired by the SIA had not received "appropriate security clearance" before starting work.
In a statement to MPs, he said: "All permanent SIA staff have confirmed security clearance.
"It became clear, however, that some agency workers had not received appropriate security clearance before commencing employment with the SIA."
Mr Campbell said the 38 workers were "removed from SIA premises and had all access to SIA systems withdrawn" while security checks were carried out.
As of 0900 GMT on Thursday, he said, 32 had received clearance and the remaining six were pending.
Mr Campbell also ordered an urgent review of any decisions taken by individuals who were not properly cleared.
The SIA authorises pub and nightclub bouncers, store security guards, CCTV operators and wheel clamping companies. It is also responsible for those employed in sensitive security posts such as bodyguards.
In October, the National Audit Office accused the authority of overspending by £17m and failing to keep track of who exactly was working in the security sector.
In a statement, SIA chairman Ruth Henig said Mr Wilson and the authority's board had come to a "mutual agreement" that he would step down.
"The board and I are grateful to him for all his hard work and dedication to the development of the SIA in the past year, and we wish him well," she said.
"An interim chief executive will join us shortly until a permanent chief executive is recruited in the New Year.
"Our delivery to our stakeholders will not be disrupted. Working closely with the industry and our other partners, we will continue to contribute to public protection through regulation."
Mr Wilson will leave his post on 13 November.
He was appointed in 2007 and before that had run the Gangmasters Licensing Authority and the Defence Vetting Agency.
The Conservatives said Home Secretary Jacqui Smith had been "staggeringly complacent" about security and accused ministers of "ducking" responsibility.
Shadow home secretary Dominic Grieve said: "This is a major breach of one of the pillars of our security apparatus and the second time it has happened on this home secretary's watch.
"Yet again she has been found trying to bury bad news rather than address the root of the problem."
Mr Grieve accused the home secretary of being "fixated on gesture politics, like ID cards and 42 days" and failing to grasp security basics.
Liberal Democrat home affairs spokesman Chris Huhne said: "This is a rare and honourable exception to the government's rule that no-one ever takes personal responsibility for anything, however damaging the blunder.
"The only way of changing the culture of carelessness about security and personal data is by making sure that heads roll when failures happen."