I have read all the dual taxation agreements and the uk one as I'm British. It only gives you a tax credit in Thailand for tax payed in the uk that's all but does not cover everything and you need to show the tax uou payed as well
the DTA only means you will get a tax credit in Thailand for the tax you payed in your own country that's all. If anyone has real ,legal and factual information about this would be interested to hear it ,