i’ve been to Thailand several times in fact more than several times with Thai air and Eva and I’ve always been led to believe through my experience that you’ve got to have onward travel in your destination country or a return ticket within the validity of your Visa whether it’s an exempt or whatever, and they don’t take into consideration any extensions that you might get, think this is a legal requirement before they let you board
Put it this way if a Thai national was flying to the UK on the one-way ticket with a tourist visa how would that work out at the check in desk?