Bit convoluted this.
We normally visit Thailand for 4 weeks, so as UK citizens (resident in France) the normal visa waiver thingy is fine. Last trip was 6 weeks and we did a 4 day trip to Cambodia in the middle, so again not a problem. We always entered and finished our holiday from Thailand so had the return flights booked when we arrived.
This time we are planing 6 to 8 weeks, with a possibility of a trip to Vietnam, and maybe Bali, in which case we would return to France from Singapore NOT Thailand. To give us the maximum flexibility, we were thinking of arriving in Thailand, but would book a return flight until we finalised our plan, so would not have a return ticket. Am I right in thinking the Thai immegration at BKK would not allow this, IE entering the kingdom, without a definitive ticket to say you are leaving?