"After she was exposed as a spy, Britain's Security Service MI5 was strongly criticized by the parliamentary committee overseeing the intelligence agencies over the failure to prosecute her."
The Europeans can't bring themselves to prosecute anyone for anything, can they?
Except that they would gladly prosecute GW Bush for nothing.
UK Security Service notes on case:
http://www.archive.official-documents.co.uk/document/cm47/4764/4764-axg.htm
"To pursue her now that the Cold War was over might open the Service up to criticism for having harassed an old lady." Aaaaarrrgghhh!
Los Alamos scientist Ted Hall, who did just as much as the Rosenbergs and Greenglass to sneak the secrets of the Bomb to Stalin, lived a very comfortable, completely open life in the UK for thirty years after fleeing there after the FBI finally caught on.