Okay, I knew I was stupid already, but if I was an assistant, and smart enough to know there was more than one London (which I've until recently not been), I'd have asked "Which one?" in case there was not enough context to make a guess. There are probably _A_LOT_ of people who have a lot more to do with the non-british London who'd be very sad indeed if The Machines (tm) suddenly decided that EVERY request about Lon…
There will be a lot more people who are asking about the British London than people who are asking about their nearest London. Apple will be making far more people sad by defaulting to the local one. If Siri asked "Which London?" every time most people would get annoyed.
What should happen from a UX perspective is that Siri should respond with "The time in London, UK, is..." which would inform the user that Siri is differentiating between different Londons, and that they need to specify a locality in order to narrow down the query to some other London if necessary. 99% of the time the user will get what they wanted first time, and the other 1% of the time the user will be informed that their query wasn't accurate enough.