Looking at the example fare* mentioned above for June, the lowest fare is non-ref but changes for 6,600THB plus fare diff. The next fare above that is fee-free changes, fare diff only. So you will need to check what you've got.




(*Incidentally it seems BA.com is quoting the price excluding TFC for this routing, not sure if that's a glitch or an ex-Thailand thing as it isn't usual.)