It comes amid worsening relations between the UK and Russia since the latter's full-scale invasion of Ukraine in 2022.
Last week it emerged the UK lifted restrictions on Ukraine using British-supplied Storm Shadow missiles on targets inside Russia for the first time.
President Vladimir Putin cited the move, alongside the launching of US-supplied longer-range missiles at Russian territory, as behind Russia's decision to launch a new hypersonic missile at the Ukrainian city of Dnipro on Thursday.
Expulsions of diplomats have become increasingly common since the war began.
Earlier this year, British diplomat Capt Adrian Coghill was given a week to leave Russia, days after the Russian defence attaché was expelled from London for alleged espionage as an "undeclared military intelligence officer".