OK they are not raising the ante- just four British diplomats unjustifiably expelled as a straight tit for tat.
Meanwhile the rest of the EU has slowly stirred themselves to mutter a bit against Russia. If there is any further problem, one would hope that a "common foreign policy" position might emerge that was a bit more proactive. Britain, Poland, Sweden, Estonia, Latvia, Lithuania now all have significant grievances with the Putinists, others too are increasingly annoyed- will Russia now calm down, if faced with a United front?
That is up to the Kremlin- but patience with Russia is wearing very thin.