Reading the Tax Guide...
TAX RESIDENCY
21) If you stay in Thailand for more than a cumulative 179 days, between 1 January and 31 December each year, you will be and always were considered to be Tax Resident in Thailand during that year, almost entirely regardless of the type of visa you have (special tax exempt classes of visa excluded). It doesn’t matter that you may be Tax Resident in your home country or elsewhere or that you pay tax in those countries, Thailand will still regard you as Tax Resident. Tax Residency and Immigration status (and the visa you hold) are different things. Tax residency is based solely on the number of days you spend in Thailand. A day appears to be counted using the entry and exit stamps in your passport, unlike many other countries where it is determined by where you are at midnight. The number of days counter reverts to zero, on 1 January each year.
So, theoretically if on a Type-O or a Type-OA for reason of retirement and I don't spend more than 180 days in the country, then funds I import into Thailand and placed in a sterling bank account here are not taxable?