What tax implications does a UK employee face when working remotely from Thailand?

I think your "tax adviser" is misleading you. If you work for a UK company and they pay you in the UK you will continue to pay tax in the UK. No way out of that unless they're willing to pay you outside of the UK. Also if you spend 180 days or more in any calendar year inside Thailand you become a Thai tax resident and you will then also need to file a Thai tax return if you bring income into Thailand. There's a dual tax agreement between UK and Thailand so you can claim a credit against Thai tax for any tax paid in the UK

So you are planning to be non-tax resident in the UK but Thai Tax Resident as your primary tax location? How will your company pay you - as an employee? Probably best to speak to a tax specialist to be honest. I have not been tax resident in the UK since 2002 and it was complex as a contractor. I was working in Belgium, being paid from Virgin Islands into a Luxembourg account. After that just an employee in Singapore and Thailand but on very low tax rates. Always had international tax accountants but company paid for them

I would consult the revenue and customs website in UK for you uk tax position. If you are in Thailand for 180 days your subject to tax on all monies brought into Thailand. You can make use of the DTA to reduce the Thai tax by subtracting what you paid in UK. The DTV is a new visa, the income tax rules in Thailand are new. No one knows how they are going to (not) work.