YMB,
You seem to be taking the Skirpal poisoning as an isolated incident, when in fact there have been 14 suspicious deaths of Russia emigres in the UK, including Alexandre Litvinenko.
His murderers were allowed to escape justice, which just emboldened the Russian State to assasinate more of its former citizens.
The reason Litvinenko was murdered is well documented...
// Litvinenko had been supplying Her Majesty’s spooks and their Spanish counterparts with hair-raising information about the Russian mafia in Spain. The mafia had extensive contacts with senior Russian politicians. The trail apparently led to the president’s office, and dated back to the 1990s when Putin, then aide to St Petersburg’s mayor, Anatoly Sobchak, worked closely with gangsters. In a week or so, Litvinenko was to testify before a Spanish prosecutor. Hence, it appeared, the Kremlin’s frantic efforts to kill him. //
I suspect a similar motive for Skirpal’s demise. The difference this time, the British Government rather than turn a blind eye like it normally does, decided to use the news to distract from the its domestic problems - a weak Government, chaotic Brexit negotiations and a split Conservative party at war with itself.
Over the pond, Trump’s White House is in similar disarry, and a spot of Bear baiting is always welcomed by a President in trouble. Hence the cranking up of the cold war, and all the expulsions.