H Robert, thanks for getting in touch rather than just changing things. Happy to change them if I've tagged them wrongly, but I'm not sure I have. I think the addr:* tags are for postal addresses and "London" is the postal town only for addresses with London postcodes - "W", "NW", "SW" etc. TW8 isn't a London postcode so it requires a different post town?
I've checked one example in this changeset in the Royal Mail "find a postcode" checker and it confirms this address:
1 Kingsleigh Close
BRENTFORD
TW8 0PA
I've used "London" for addresses just over the border in Ealing because they do have a postcode relative to London.
Let me know if you think this is still wrong.