BTW the above info re: TWOV (Transit Without Visa) comes from Transit (INF 20) straight off the UK Border Agency website.

Jazzbo, yes I was aware that Thai nationals can transit the UK without a visa in the circumstances you describe and my answer was misleading, but I was assuming that having flown nearly half way round the world somebody would want to stop off in the UK for a couple of days to at least relax, especially as the whole purpose of this trip was family celebration and applying for a UK Visa in these circumstances is far less arduous.

I accept I wrong in making these assumptions.

OK K. Git -- Transiting London is really little difference from the usual American requirement to transit Tokyo or Taipei, etc. (other than the TG non-stop to LAX) ...

Bermuda is 11 GMT zones different from Thailand ...

When people in USA say 'Thailand ... how far is that?' I say that it is 12 time zones away from EST which is as far as you can go or else you are coming back!