Needless to say, while the official was presumably off leaving trade secrets and government intel in taxis and buses, a passenger on the train noticed the file with "Top Secret" printed on its cover and decided, as any good law-abiding citizen would, to hand it in to the local authorities. Wait, did we say local authorities? We meant the BBC, one of Britain's largest media outlets.
The Sun is a smaller outlet, but undeniably the better news source.
The BBC, possibly deciding that "for UK/US/Canadian and Australian eyes only" included them, read through enough of the reports to say that they would have been incredibly damaging had they fallen into the wrong hands. At that point, they most likely used the information to produce a sitcom that, in a few years, will be remade in the US to much greater (or lesser) success. That's just how foreign relations work.