Britain’s Nato envoy Angus Lapsley, 55, has been told to stop living with his Italian girlfriend, 29, at his official residence.

Concerns were raised after Mr Lapsley began to share his official residence with the woman, whom he met at Nato’s headquarters in Brussels while she was just an intern.

The UK’s incoming ambassador to the EU, Dame Caroline Wilson, said it was “inappropriate” for the pair to live together there.

The father-of-two’s relationship was considered a significant point of concern, and was raised to Admiral Sir Keith Blount, the deputy supreme allied commander in Europe and most senior British officer in Nato.

After a review of Nato’s relationship policies, it was deemed he had not broken any guidelines and allowed to continue in his post, later promoted by the British Government to ambassador.

Nato does not have any rules on relationships with subordinates, unlike the British Armed Forces, where they can be a sackable offence.

Admiral Sir Ben Key, the former First Sea Lord, was thrown out of the Royal Navy last year and stripped of his rank after he had an inappropriate relationship with a subordinate.

On Tuesday night Mr Lapsley pulled out of a briefing at Nato headquarters as the Foreign Office prepared for details of his relationship to be made public.

One source said the relationship was an open secret in Brussels.

They said: “They have made no attempt to hide their relationship. Angus used the residence as if it was his, and [the woman] was there [for] Christmas and summer receptions.”

The long-serving civil servant separated from his wife Gina before moving to Brussels in 2022.

Mr Lapsley was promoted to the role of ambassador to Nato despite leaving 50 pages of documents behind a bus stop in Kent in June 2021.

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The documents contained the locations of British special forces in Kabul, Afghanistan, and the Royal Navy’s movements in the Russian-occupied Crimean peninsula.

This angered the Americans – who were concerned the breach could endanger US soldiers.

After the incident, Mr Lapsley’s security clearance was suspended, but later reinstated after an investigation.

One Ministry of Defence source told the Times that Mr Lapsley also left behind a personal diary.

Sir Ben Wallace, the Defence Secretary at the time, called for his security to clearance to be reconsidered after the 2021 incident.

The diary reportedly contained thoughts about his frustration at the department and his relationships with individuals.

Sir Ben said of the diary: “It is not acceptable that the Foreign Office and others persisted to ignore concerns raised by me and others about this individual. Officials, by ignoring ministerial direction, have now risked the UK’s reputation in Nato and undermined security.”

A Foreign Office spokesman said: “It is longstanding policy not to comment on personnel matters.”