Just to clarify for any UK Expats with UK sourced pensions that are taxed in the UK and then those pensions are remitted to Thailand and are classed as taxable income in Thailand. I believe the relevant clause in the DTA is "Article 23 Elimination of Double Taxation, item 3" quoted below:
"(3) In the case of Thailand, United Kingdom tax payable in accordance with this
Convention in respect of income from sources within the United Kingdom shall be
allowed as a credit against Thai tax payable in respect of that income. The credit shall
not, however, exceed that part of the Thai tax, as computed before the credit is given,
which is appropriate to such item of income."
My interpretation of this article is that you can quote this to the TRD and claim any UK paid tax as a credit against your Thailand income tax liability - providing it is the same income in both countries. My understanding is that the credit amount is put in Thai Personal Income Tax Form 90 under "Item 11.13 Computation" and I guess if the TRD query this you quote the DTA with proof of UK tax paid.
Jojothai - I agree there has been a lot of misunderstandings in previous posts but I believe the above is correct. - hope this can help clarify the tax credit applicable in Thailand.