Britain has threatened to shut down the Russian trade mission in north London, describing it as a “den of spies” as diplomatic tensions between the two countries reached a new height.

London escalated the row between the two countries after Moscow said more British embassy staff would have to be expelled from Russia as the fallout from the Salisbury poisoning intensified.

That came after Russian officials accused Britain of "provocation" following an enhanced search by a "rummage team" of UK border officials of an Aeroflot flight from Moscow.

The Russian government has four bases in the UK: its embassy, a consulate and a trade mission in London and a sprawling country estate in the Home Counties.

British government sources on Friday night told The Telegraph that the UK was looking at shutting down the trade mission in Highgate, north London.

The mission is a base for many Russian officials. One source said losing the trade mission “is something we will look at”, adding: “The Highgate one is a den of spies.”

Shutting the trade mission in Highgate would be seen as evidence of Prime Minister's Theresa May’s pledge to consider more measures after Russian closed down the British Council earlier this month in the wake of the tit for tat diplomatic expulsions.