In a major security breach, Britain’s overseas spy agency MI6 chief’s cover has been blown after his wife published family holiday photographs and other personal details on social networking site Facebook.

Sir John Sawers, currently Britain’s ambassador to the United Nations, is due to take over as chief of the Secret Intelligence Service in November, putting him in charge of all spying operations abroad. But his wife’s entries on the social networking site have exposed potentially compromising details about where they live and work, who their friends are and where they usually go on holidays.

Lady Shelley Sawers put no privacy protection on the account, meaning that any of Facebook’s 200 million users in the ‘London’ network could see the entries, no matter where they were in the world, the Daily Mail reported.

The lapse revealed the couple’s friendship with senior diplomats and actors. And it revealed the spy chief’s brother-in-law who holidayed with him last month, is an associate of the controversial Right-wing historian David Irving.

However, after the British newspaper alerted the Foreign Office to the astonishing misjudgment, all trace of the material — which could potentially be useful to hostile foreign powers or terrorists — was removed from the Internet.

Some politicians called the details a security lapse - but others said they revealed nothing but a few mildly embarrassing domestic details. Foreign Secretary David Miliband said, “It’s not a state secret that he wears Speedo swimming trunks”. “For goodness’ sake, let’s grow up.”

Until the 1990s, the identity of the MI6 chief, known as C, was kept secret. Until 1992, Britain’s government refused even to confirm the organization’s existence. Authorities have gradually become more open about MI6 and its domestic sister service MI5 in a bid to shed the agencies’ cloak-and-dagger image and attract a wider range of staff.