The closest place this chemical could have come from is HMG's Porton Down research establishment, 6 miles from Salisbury which and known to hold stocks of the stuff used to try and develop an antidote. I do hope plod have examined the records of stock in, out and used and the movements and records of all the staff who had access to this agent.
Has Mrs May asked this question? If not why not?
Then we have the front page story in today's DT that the agent was planted in the daughter's luggage before she left Moscow. This is easily the most likely explanation but who planted it in the luggage, at Moscow the Russian state or the Russian Mafia? The DT claims that a gift, an item of clothing or cosmetics could have been contaminated with this agent. The item would have to have been touched by the daughter or the father or both. These substances generally need skin contact to work but is then easily spread by fingers hence the contamination of the cafe chairs and table and the unfortunate DS. The package must have been opened to work but the only two people who can shed any light on this are unconscious and may not recover.
The aspect of this scenario that worries me most and I am sure worries Mrs May most is if the luggage containing this stuff had opened in the UK airport terminal there would have been mass slaughter. I think of the rigmarole of going thru airport security taking off your belt shoes etc all rendered useless by the simple expedient of planting a small amount of odourless powder in a suitcase. Sniffer dogs detect drugs but can they detect nerve agents or like canaries in mines die in the line of duty.
I am quite sure airport security will be tightened after but how effective will it be? Mainly cosmetic is my view. We will never know who planted the agent. Again the terrorist are one step ahead and we are fighting the last war ie terrorists blowing up airliners. These nerve agents could shut destroy a whole airport but don't worry Jezza will negotiate whilst Rome burns.