martinplas

I'm flying Today on a United First class redemption IAH – LHR – BKK-CNX. I'm on United metal to London Heathrow ,where I picked up Thai First for the rest of the trip to Bangkok and Chang Mai.
I have a couple questions that I can't seem to get an answer:
1) do I clear immigration in Bangkok or Chang Mai?
2) when I get to London which first-class lounge will I be able to use. My
status is United Silver elite so no benefit their. I'm sure I can use the Global First Lounge but what about Singapore?
3) United has only issued the boarding passes to Bangkok. As another piece of paper that says they can't issue a boarding pass for that portion of the flight. See the ticket counter at the airport.do I need to leave the secure area of BKK airport to go to the ticket counter or can they do that in the Thai Club Lounge
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co plat,hilton gold,starwood gold

THD

non-EU to non-EU transfer at LHR actually involves a passport check and security, even within the same terminal. Basically you will land at Terminal 2B and need to walk all the way to Terminal 2A for the check and then walk all the way back to Terminal 2B.

Otherwise at Heathrow the Singapore Airlines Lounge has not yet opened in terminal 2, so the options are either the United Glocal First Lounge or the Air Canada Maple Leaf Lounge. Both of which you will have access to via your boarding pass, irrespective of your status.

BinSabai

1) Bangkok, immigration for transiting passenger at intersection A/B/C/D (East) terminal (NOT for those with final destination in BKK); but you should check your luggage through to Chiang Mai; there you will arrive in international arrival and go with your luggage through customs
2) answered
3) at transit counter in arrival area close to immigration for transiting passengers