I visited the Nathon branch office today and although they were very friendly and eager to help, they had no English so conversations were held through Google translate. Eventually, after 1 hour they told me I didn't have to fill in a return. Being cautious of this, I asked for the decision in writing. They escorted me to the headquarters of the Revenue Department on Samui and into the office of the director himself.
He was very friendly and helpful,(even offered coffee). His English was perfect.
Results as follows,(this applies to UK pensions)
1. UK old age pensions ARE TAXABLE in Thailand , if remitted, and are part of your total assessable income.
2. Government service pensions are not assessable and do not have to be declared,
even if remitted, but proof of source may be required if audited.
3. Allowable deductions for the year:
a) B60k personal allowance.
b) B100k for expenses,(this is a blanket allowance and does not require any proof of expenditure).
c) B190k if you are over 65yrs. of age
Once you have deducted these from your assessable income you then get the 1st B150k at zero rate of tax. If after that you still have a positive balance you MUST file a return. If there is no balance left, you do not have to file a return but can if you wish.
If. You wish to offset UK tax already paid, this should be filed along with your return, enclosing proof from the relevant authority. There is no space on the tax forms specific to this.
Hope that makes things clearer.