Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question. By the way, I have a Thai wife.
Firstly, when you left the UK for the Kingdom, did you send a Form P85 to HMRC? If you did not you should do so immediately. Fortunately there is no time limit as to its submission, it is available on the net and can be filed on line. On receipt HMRC will classify you as non resident for the next financial year and furthermore split the leaving year into two parts, one resident and the other non resident. You will find dealing with that Department much easier if you complete this form. Once you are classified as non resident you can spend up to 91 days in the UK in any one tax year without breaching your non resident status.
Unfortunately, it is normal for pensions to be taxed in the country of origin and individuals have to rely on Double Taxation Treaties to avoid being taxed twice. As I understand it Thailand only taxes ex pats on moneys earned or brought into Thailand and it does have a Taxation Treaty with the UK. The treatment of your draw downs, which since recently you would have been taxed at 55% due to your age (you can only draw down over 55 without massive tax penalties now) would appear to be correct. 25% of your pension pot is tax free, the balance being taxed at your marginal rate. This may have pushed you into the top tax bracket at 45%. Also if your taxable income exceeds 100K you loose your personal allowance at the rate of one pound for every two quid over.
However, there is normally no tax rate of 50%, so there appears to be something wrong there, the additional rate being set at 45%. You can find the current rates of tax here:
You should take up with your tax office the apparent discrepancies and seek a refund.
I do hope that I have shown you a way forward in this matter and shed some light on your situation.