@Bob *********
You are American, so come from a strange country, which levies taxes on all US citizens, whether resident in the US or not. You question is irrelevant to the topic which is about UK-Thailand taxation. You should start your own thread, though I suspect the reason why you are not facing a Thai tax bill in the tens of millions is buried in the tax treaty Thailand has with your country. I don't know why you have lived in Thailand for 15 years. I don't know why, despite being registered with the Thai tax authorities since you are a law abiding resident of Thailand, they have not approached them about the subject. Maybe you should ask them.