The wife of the new head of MI6 has caused a major security breach and left his family exposed after publishing photographs and personal details on Facebook.

Sir John Sawers is due to take over as chief of the Secret Intelligence Service in November, putting him in charge of all of Britain’s spying operations abroad.

But entries by his wife Shelley on the social networking site have exposed potentially compromising details about where they live and work, their friends’ identities and where they spend their holidays. On the day her husband was appointed she congratulated him on the site using his codename “C”.

Lady Sawers had put virtually no privacy protection on her account, making it visible to any of the site’s 200m users around the world who choose to be in the open-access London social network on Facebook.

The extraordinary lapse exposed the couple’s friendships with senior diplomats and well-known actors, including a leading character in The Archers, the BBC Radio 4 drama, and revealed that the intelligence chief’s brother-in-law, who holidayed with him last month, is an associate of David Irving, the controversial right-wing historian.

Once the Foreign Office had been informed of the faux pas all the material was removed from the internet. The move suggests that MI6 or the Foreign Office had not vetted the information the Sawers family shared over the internet.

Foreign Office staff are warned about using social networking sites when they join but MI6 advises its agents to maintain even tighter secrecy, telling them to reveal their true role only to their closest family.

Last night Ed Davey, the Liberal Democrat foreign affairs spokesman, told The Mail On Sunday: “This type of exposure verges on the reckless. The prime minister should immediately commission an internal inquiry as to whether this has breached the security of the incoming head of MI6 too seriously to allow him to take up the post.”

The Tory MP Patrick Mercer said the MI6 chief had left himself open to blackmail. A Foreign Office spokesman was unavailable for comment last night.

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