There's a number of factors to be considered. Have you already paid tax on the gain? Are you a UK tax resident? What does the UK DTA say about transfer of capital gain? My question is why would you transfer such a large sum of money to Thailand when you can get much higher return in the UK? I only transfer pension from Australia which is tax exempt, plus I also retain Australian Tax Residency and under the terms of the DTA, the Australian Tax Office has sole taxation rights.
With bank interest, the tax is deducted at the source, so unless you wish to claim it back, there's no tax issues with bank interest. I'm on the monthly transfer method and that suits me, as my Australian Super Fund pays between 8 and 9 percent per annum tax free, which is around
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k baht per year. I get a decent health insurance cover for less than that, so that's my bonus