The Russian foreign ministry said staff from the UK’s Moscow embassy would be “declared persona non-grata” and expelled within a week.
It also said it would close the British Council in Russia, which promotes cultural relations between the states.
The move comes in response to Britain’s decision to expel 23 Russian diplomats.
They were ordered to leave over the incidenton 4 March which the UK government has blamed on Russia – but which Russia strongly denies.
Russian ex-spy Sergei Skripal, 66, and his daughter Yulia Skripal, 33, remain critically ill in hospital, after they were found unconscious on a bench in Salisbury, Wiltshire.