Labour MP Tom Watson has called for all details of Andy Coulson's security vetting by the government to be made public, after the former Downing Street head of communications told the Leveson inquiry that he may have seen top-secret documents which he didn't have the right security clearance to view.

Andy Coulson did not have the higher level of security clearance - know as "developed vetting", enjoyed by previous Downing Street heads of communications such as Alastair Campbell. Instead he was only on "security check" status, which meant he had been subject to a degree of vetting.

Why this would be the case remains unclear, as does apparent contradictions between government statements surrounding Coulson and his evidence, both written and verbal, to the Leveson inquiry.

Coulson told the inquiry in a written statement his previous level of security clearance would allow occasional access to top-level paperwork and participation in secret meetings. He said when he arrived at Downing Street he did not ask what level his clearance was and assumed it would be the appropriate level.

"I should say that I never asked for special access and did not ask for special authority over the Civil Service," he wrote in his statement.

"I went to the meetings I was invited to and got on with my job."

When asked at the Leveson Inquiry on Thursday whether he'd had ever had access to top-secret documents, he said: "I may have done, yes."

This seems to contradict previous Cabinet Office statements about Andy Coulson, chiefly that: "No information is held that shows that Andy Coulson was sent information incorrectly or for which he was not authorised."

Labour MP Tom Watson has previously submitted freedom of information requests to the government about Andy Coulson's security clearance. He told HuffPost: "There must be an internal email trail concerning the answer to a Freedom of Information request on Andy Coulson's security clearance.

"People deserve to know how Mr Coulson was able to read documents he wasn't cleared to see. There was clearly a security lapse at the very heart of government. The Cabinet Office should provide all emails, documents, notes and minutes concerning this matter to Lord Justice Leveson, so that he can establish the facts of the case.

"Just why did Andy Coulson not go through Developed Vetting?"