Diplomatic vehicles drove them from the embassy in London to Stansted Airport, where they boarded a plane to Moscow.

The UK expelled 23 diplomats after Prime Minister Theresa May said Russia was "culpable" for the poisoning of Sergei Skripal and his daughter.

The government decided on Tuesday not to impose further sanctions on Russia for now.

However, at a meeting of the National Security Council, Mrs May said: "There are other measures that government and security officials are actively considering and stand ready to deploy at any time."

Strict checks by border officials on private flights have been introduced as the UK increases efforts to monitor and track those entering the country, Mrs May's spokesman added.

Moscow has denied all involvement, and is expelling 23 British diplomats in response. The UK diplomats have until Saturday to leave Russia.