James Roscoe had served as deputy ambassador to US since 2022 and stood in after Peter Mandelson’s departure

Britain’s second most senior diplomat in Washington, who stood in as interim ambassador after the sacking of Peter Mandelson, has abruptly left his post.

The UK government gave no reason for James Roscoe’s sudden departure, which comes amid an investigation into the leak of discussions at a meeting of the UK’s national security council.

A Foreign Office spokesperson said: “James Roscoe has left his post.”

Roscoe had served as deputy head of mission at the British embassy since 2022 and was among those tipped for the ambassadorial job after the removal of Mandelson. The posting ultimately went to another career diplomat, Christian Turner.

Senior officials at the embassy are said to have been among those questioned as part of an investigation after reports this year of cabinet splits at a national security council meeting over allowing the US to use British bases for strikes against Iran.

Those discussions are protected by the Official Secrets Act and a leak from the national security council is considered a serious breach. In 2019, Theresa May sacked the then defence secretary, Gavin Williamson, over a leak.

David Lammy, the justice secretary, ordered an investigation into the apparent leak of the discussions this year. The Spectator reported that Keir Starmer suggested allowing the US to use the bases to carry out defensive strikes against Iranian targets at the meeting but was met with opposition from Ed Miliband, Rachel Reeves, Yvette Cooper and Shabana Mahmood. The report was then picked up by several other media outlets.

As chargé d’affaires to the US, Roscoe played a key role in Donald Trump’s state visit to the UK in September 2025. More recently, as second in charge at the embassy, he was involved in King Charles’s state visit to the US to mark the 250th anniversary of American independence.

Before moving to Washington, Roscoe was the UK ambassador to the UN, and he previously served as communications chief to the Queen Elizabeth II from 2013 to 2016.

He had also been chief press officer in Downing Street for the prime ministers Tony Blair and Gordon Brown. Roscoe’s earlier diplomatic postings included Sierra Leone and Iraq.

Roscoe was reported to have seen himself as being on the operational side of “cleaning up the mess” in terms of relations with the White House rather than acting as a figurehead of UK relations.

Source: https://www.theguardian.com/politics/2026/may/20/british-diplomat-james-roscoe-abruptly-leaves-washington-embassy-post