The Brits are being subjected to a barrage of Russian-origin fake news denying Russian responsibility for the poisoning with a military grade nerve agent of a former spy and his daughter. This propaganda is not so much designed to change minds about "who done it" as to make people feel they cannot possibly know what is true. This is a signature tactic of modern dictatorships -- people get worn out amid the chaos and look away. This is not the same thing as responding to citizens' honest desire for evidence, either. It's noise to drown out understanding.
So the British Foreign Office has struck back not with refutations but with mockery. Enjoy.
H/t Anne Applebaum.