Andy Coulson did not face the rigorous government security checks into his background that most recent Downing Street press chiefs have undergone, it emerged on Wednesday.

The former News of the World editor was granted only mid-level security clearance when he was appointed by David Cameron as his director of communications, so avoiding "developed vetting" involving a detailed interview by government investigators looking for anything in his past that could compromise him.

The checks would have involved a review of his personal finances and cross-examination by investigators of referees, who could include friends and family. Coulson would have been asked by government vetters, some of whom are former police officers, such questions as: "Is there anything else in your life you think it appropriate for us to know?"

Alastair Campbell and Dave Hill, who ran communications for Tony Blair, and Michael Ellam, who did the same job for Gordon Brown when he was prime minister, were all subject to the more rigorous checks which are said to be in part targeted at uncovering potentially damaging secrets in an employee's background.

In the Commons, Cameron said Coulson had gone through the "basic level of vetting" and was not able to see the "most secret documents in government".

The prime minister added: "It was all done in the proper way, he was subject to the special advisers' code of conduct."

The disclosure will fuel suggestions that Cameron failed to take proper steps to check allegations that Coulson had been involved in illegal behaviour at the NoW.

The Cabinet Office denied that Coulson was spared high-level security vetting to avoid any potentially embarrassing information coming out which could have compromised his appointment.

A spokesman declined to comment in detail on Coulson's security status but said he would have been consulted by a senior official over which level of vetting he should undergo. "In normal circumstances at a senior level the postholder would be consulted. You get the standard level and you discuss whether to go higher."

Jonathan Powell, Blair's former chief of staff, said: "In our time in No 10, the press officers were all cleared at the highest level. It is essential if you are going to work on international matters to be able to read intelligence and other relevant material."

The Cabinet Office said that, unlike Campbell and Powell, Coulson's job did not require him to have high-level security clearance. He did not attend cabinet meetings, the bi-weekly national security council meetings, or Cobra, the government's emergency committee.

"He had 'security check' level of security clearance which most officials in No 10 and most special advisers would be subject to," a spokesman said. "The only people who will be subject to developed vetting are those who are working in security matters regularly and would need to have that sort of information. The only special advisers that would have developed vetting would be in the Foreign Office, Ministry of Defence and maybe the Home Office. Andy Coulson's role was different to Alastair Campbell's and Jonathan Powell. Alastair Campbell could instruct civil servants. This is why [Coulson] wasn't necessarily cleared. Given [the nature of] Andy Coulson's role as more strategic he wouldn't have neccesarily have been subject to developed vetting."

Coulson was also screened by a private company when he started working for the Conservatives in 2007. Asked in the Commons, Cameron refused to name the firm involved.

Electoral Commission returns show that the party last year used Control Risks Screening to vet several staff at a cost of £145.70 per check. If this is the level of vetting undergone by Coulson it is likely to have involved only the most cursory checks of online records.

The party said last night it would not comment on the company or the level of scrutiny involved in Coulson's clearance, which involves a check of health records, police files, financial history, MI5 records and possible interview if recommended by the security service.