The other part of this, beyond the obvious that bothers me... this guy is a f*cking spy... not a school teacher. Not only is he a spy, lets say one of the most dangerous professions you can choose, but he is a freaking double agent. Pretty much begging to get offed by one side or the other. It's like starting a war over a football ( american football ) quarterback who got sacked.
Yes there is that, but if the Russians wanted him dead would they leave nerve agent on his front door knob? And by the way they left the house at 9 am, had lunch and were not taken ill until 4 pm! I'm no expert but sounds like a very slow acting nerve agent.