I am not surprised there are posters who believe in conspiracy theories ...
Personally I am neither interested in "conspiracy theories" nor am I interested in the mud slinging about conspiracy theories. I am interested in evidence and so will other countries be. If we want to take the organisations we belong to, and other countries, with us on this we will have to supply that evidence so why not have a realistic attitude to it in this country.
What we have been told is that the Russian's originally made this - and that no one else did. It is reasonable, therefore, to believe that, either the Russian state attacked a British citizen on British territory with this or they allowed it to get into the hands of someone else who did. Whatever we may think, feel or wish to be true we do not know more than that. We do not know it was government sponsored. We do not know if it was a rogue group. It could still, on the evidence we have, have been either. We have, so far responded appropriately to that knowledge and that response has had the full and complete backing of both sides of the government.
To be honest that leaves me with only one question. What is your problem?