How does the 180-day tax rule affect my DTV application from the UK while running a business remotely in Thailand?

The rule is not 180 days per year. When you leave the country and come back, this can be on the same day even, you get the next 180-day stamp in your passport.

If you pay taxes in the Uk, it’s very unlikely you will have to pay taxes in Thailand due to double taxation treaties.

If you’re hiding your assets in a tax haven and not paying any taxes, Thailand will want a piece of anything you’re bringing into the country

The 180 days is cumulative not consecutive in a calendar year. It does not reset just because you fly out.

The rule is 180 days per year in Thailand, it doesn't change anything if they are consecutive or not, it is cumulative. However, the UK signed a DTA with Thailand to avoid double taxation, i suggest you take a look on it.

I would not be thinking too much about the Thai Tax situation at the moment. Even if in Thailand and tax resident in 2025 tax submission not due to till March 2026. Wait and see how it pans out for those on O visas. Even if yiu are Thai Tax Resident only monies remitted to Thailand are assessable. The UK also has a double taxation treaty with Thailand - read that. So lets say you earned in UK and were taxed on it in UK. Depending how much you remitted to Thailand you may owe some Tax here depending on allowances, and tax rate differentials. Unless you are planning to bring in a lot of money I would not worry. If you are bringing in large amounts consult an international tax consultant.