In TL you have to make the first move, so you have to go to your revenue office and ask for tax ID, and next year you will have to go to the revenue office again and ask for the tax filing forms. The revenue office will not inform you personally or send any letters. TIT
first: I don‘t know how much a state pension in UK is in sum. As you live more than 180 days in Thailand you wouldn‘t be taxed in UK anyway no matter how much your pension is. Your pension might be below threshold in UK but if you transfer it to Thailand its probably high enough (above 150‘000 thb) to be taxed.
You can‘t stay here in Thailand anyway if you haven‘t either 800‘000 deposit or a monthly income (pension) of 65‘000 thb.
Where did you get this information? I got a completely different answer. Of course retirees who stay here for over 180 days and have income from overseas like pensions, they haven‘t payed tax yet on them and tranfering to Thailand have to pay tax.