Parliament's security watchdog has launched a probe into 'cover-up' claims around the resignation of GCHQ boss Robert Hannigan first revealed by The Mail on Sunday.

Mystery surrounded the 2017 departure of the spy chief until this newspaper discovered he had helped a paedophile priest escape jail by giving him a character reference, only to see him reoffend.

Theresa May was accused of a cover-up after allowing the powerful director of Britain's listening station and largest spy agency to quietly resign when alerted that Hannigan's connection to Father Edmund Higgins had been unearthed by a sister intelligence agency.

Parliament's security watchdog has launched a probe into 'cover-up' claims around the resignation of GCHQ boss Robert Hannigan who helped a paedophile priest escape jail

At the time of his departure, Mr Hannigan had cited 'family reasons', with the crucial Higgins link kept secret even after the paedophile was jailed for child abuse in 2018.

Now Parliament's intelligence and security committee is investigating whether the Mr Hannigan – at the time a Foreign Office official – used Foreign Office headed notepaper for the 2013 letter defending the disgraced priest, a family friend.

He wrote it shortly before he was promoted to his role at GCHQ and the letter helped Higgins receive a suspended sentence.

Within months, he went on to reoffend by peddling sick online child abuse images, before being snared by the National Crime Agency.

Security sources confirm the committee is probing the incident, with members furious they were 'kept in the dark about a serious national security incident'.