It's risky. For me, it would all depend on what's at stake with your onward connection out of BKK. If there are plenty of alternative options later on, then I'd take the risk. If not and it would severely disrupt your itinerary, then I'd rebook a better connection.

I guess this might be EK30 connecting to EK376. I'd give it a 80 to 90% chance of success (London flights are unfortunately not immune to delays... If you were on EK30 last Sunday, you would have not made it). Misconnecting would mean getting bumped to EK370 which lands in BKK at 18:20 (assuming there is availability). What would this do to your connection? Any later alternatives?