The Metropolitan Police has launched a criminal investigation into the alleged leak of diplomatic emails from the UK ambassador in the US, which were critical of the Trump administration.
Assistant Commissioner Neil Basu said there was a « clear public interest » in bringing those responsible to justice.
Sir Kim Darroch stepped down as ambassador on Wednesday, saying it was « impossible » for him to continue.
President Trump had earlier said the US would no longer deal with Sir Kim.
The US president branded him « a very stupid guy » after confidential emails emerged where the ambassador had called his administration « clumsy and inept ».