https://onlinelibrary.wiley.com/doi/abs/10.1002/rcm.7757
https://analyticalscience.wiley.com/do/10.1002/sepspec.1591c...
I am pretty sure that the Porton Down military research facility next to Salisbury is capable or producing it too - but that doesn't mean they produced the specific poison used to attack the Skipals.
The same for VX gas that was used to kill Kim Jong Un's brother in Malaysia. VX was indeed invented by the brits but I would seriously doubt that they killed Kim Jong-Nam.
Edit: this is just factual information. What kind of fscking loosers do downvote this? Go get a reality check.