A Foreign, Commonwealth and Development Office spokesperson confirmed that Roscoe has left his post but did not immediately respond to further questions.
Two people briefed on the matter told POLITICO that Roscoe had faced questions as part of an inquiry into leaked details from an NSC meeting about the war in Iran.
A third person, a U.K. official, described the matter as “extremely serious.”
His involvement in the inquiry was first reported by The Times.
The Spectator reported in March on splits in Keir Starmer’s Cabinet at the top secret meeting over allowing the U.S. to use British bases for the strikes against Iran — a confidence breach described by Deputy PM David Lammy as an “absolute travesty.”
Roscoe’s departure comes shortly before another potentially embarrassing release of files relating to Mandelson’s time as top envoy to the U.S., and deals yet another blow to Britain’s damaged diplomatic service.