Exclusive: Opinions split on ‘unprecedented’ release of files, despite demand for ‘all papers’ related to ex-US ambassador’s appointment

• Revealed: Mandelson failed vetting but Foreign Office overruled decision

• Five key questions: who overruled decision to deny Mandelson security clearance?

Senior government officials have been considering whether to withhold from parliament sensitive documents that show Peter Mandelson failed security vetting before he assumed the role of US ambassador, the Guardian can reveal.

Any such decision could amount to an extraordinary breach of a parliamentary vote that ordered the release of “all papers” relevant to Mandelson’s appointment.