The cheapest London to Chiang Mai return flight on the radar right now is £383, flying with Air China via one or more connections. It covers departures in October 2026, and every dated link below opens that exact LHR–CNX search on Skyscanner. At 31% under the £557 we normally record here, it is one of the strongest LHR–CNX fares in our index. Across 71 recorded checks it has ranged between £372 and £643. Our sampling points to October 2026 as the cheapest month to fly London to Chiang Mai.
Prices are re-checked against Skyscanner automatically, and every one shows when it was last confirmed, so nothing here is older than it looks. Not flying from London? We track 50 other departure cities for Chiang Mai, listed at the foot of this page.
Prices like this tend to vanish fast. If it has gone when you look, try the days either side of the dates above, since London to Chiang Mai is often still worth booking within a day or two of the fare we found.