The correct answer to my question is (if you go 40 rather than 20 years) that the bodies are very much buried in Northern Ireland (although the FRU was part of the British Army)
https://truepublica.org.uk/united-kingdom/britains-secret-as...
The Russians have always been much better at espionage than the west, that's why they're bolder with these public hits.
It is indeed fuzzy
There is NO logic to violating the Universal Declaration of Human Rights, nor any of the myriad laws against extrajudicial killing, rendition and torture. It defies logic, unless the real intent is to foment the conditions ripe for yet more, endless war.
Also I think espionage is (and I think I agree, the Soviets were better at infiltration probably) orthogonal to bold public hits. The public hits are an intimidation tactic.