Twenty-three Russian diplomats and their families have left the UK in a dispute over the poisoning of a former spy in Salisbury. Britain accuses Moscow of using the nerve agent Novichok in an attack on Sergei Skripal and his daughter, who are still critically ill in hospital.

Moscow denies the claims and has retaliated by forcing the same number of British embassy staff to leave Russia.

Al Jazeera's Barnaby Phillips reports from London.