So I have been thinking the same question, as I plan to come to Thailand next year on a DTV, and assessing whether I stay longer than 6 months in a calendar year, or bounce around other parts of SEA for 60-90 day stops before returning to Thailand on 1st Jan 2027.
Anyway, I found a helpful video on YouTube that clarifies the DTA situation between the UK and Thailand. Of course, this is officially the letter of the law...but whether it's even remotely enforced is another question entirely. Even more interesting if what the other poster said is true about rule-changes to remitted income derived from overseas.
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