There are many Russian agents in the UK that MI5 is aware of. They mostly watch and monitor them to see what the hell they are up to. Perhaps a few should die via tragic accidents or just a single 22 long rifle slug to the head fired at close quarters. This would send a message to Russia that is clear and simple. Do not kill in our nation!
One of the many strange features of the nerve gas poisoning in Britain is that no one seems to have died, yet. Despite the alleged use of one of the most toxic of chemical weapons. Nor can the British government say where the poisoning took place, or how it was administered.