A "FRAT house" atmosphere in Boris Johnson's flat and laxness around security led to restrictions on where top-secret papers could be viewed, it has been claimed.

Highly classified material was left lying around in 11 Downing Street where it could be read by any visitor, reported The Times.

Sue Gray, who is investigating lockdown parties held in Downing Street, found that some of Carrie Johnson’s friends had access to a Pin code giving access to the private flat above 11 Downing Street, according to claims being made in Whitehall.

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Then top adviser Dominic Cummings is said to have found “STRAP” material lying around the flat in early 2020 – highly classified documents which only named individuals can view often requiring security clearance above Top Secret.

The National: File photo dated 25/5/2020 of Dominic Cummings who claims that Boris Johnson's Downing Street is now a branch of the "entertainment industry", with a lack of serious focus on important issues. The Prime Minister's former chief aide used

The papers can easily be spotted as they are printed on pink paper, and were also allegedly found at the upstairs quarters in Chequers, the Prime Minister’s country house.

Cummings and Johnson’s principal private secretary Martin Reynolds responded by having Johnson sign sensitive papers in his office before they were returned to a safe location.

One source told The Times that Johnson’s ministerial box with crucial documents was left outside his flat’s door on Saturdays, “often” from the morning until evening.

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Another described the scene in 11 Downing Street where Carrie entertained friends as “a frat house”.

A former No 10 official said: “Cummings was dismayed that very highly classified STRAP material was not kept in the PM’s box but was lying around the flat, and upstairs in Chequers, in such a way that Carrie could see it and potentially her journalist friends and other guests when they were invited to the flat and Chequers. There had been a series of leaks of national security issues.”

A spokesman for No 10 did not say whether the extra security measures around the papers were still in place.

He said: “We do not comment on security matters.”