Andy Coulson was not given top-level background checks

Andy Coulson underwent only mid-level security vetting as David Cameron's communications chief at Downing Street.

That spared him the requirement of undergoing much more comprehensive and rigorous checks on his background. Had he been put through the higher level of security vetting there would have been detailed background checks on his finances and intensive interviews designed to find out if anything in his past might embarrass the Government.

His predecessors, Alastair Campbell and David Hill, who were Tony Blair's communications chiefs, and Michael Ellam, who was Gordon Brown's, all underwent the higher-level vetting. Mr Coulson's lower-grade clearance surprised some Whitehall insiders, who said that without a higher level of clearance he would have been barred from knowing much of the information that people like Mr Campbell would have regarded as essential to their jobs.

But the Cabinet Office said his job was different from Mr Campbell's and did not require him to attend events such as Cobra sessions and Cabinet meetings.

Crucially, Mr Coulson did not have the authority to order civil servants about, whereas Mr Campbell did.

Mr Cameron told the Commons yesterday that Mr Coulson had undergone "basic level" vetting and that he would not have been privy to the Government's most secret information. He added: "It was all done in the proper way, he was subject to the special advisers' code of conduct."