I'm flying into Heathrow from Bangkok on Thai Airways, arriving at 7:15am. I want to catch a BA flight to Istanbul departing 10:30am. Will I have enough time? I'll need to get my luggage, possible change terminals and check in for the BA flight. I don't know which terminals each flight will use!
Three hours should be enough time. Check with Thai Airways to see if they have a baggage agreement with BA; they probably do. This way you don't have to recollect your luggage it will be automatically sent to your connecting flight. To check-in for your BA flight, head to the transfer desk to get your boarding pass; you won't have exit the terminal.
Great! Thanks so much for your very speedy answer. I'll check with Thai Airways, as you suggest.
You will arrive at Terminal 3 and depart from Terminal 5. For instructions on making this connection, go here.