I agree with
@London ****
getting a 90 day single entry Non-O visa in the UK using the eVisa system is NOT difficult and you can show funds in your UK account to get it
Then when you come in you'll get stamped in for 90 days and have time to get a bank account opened get the 800K baht in it and let it season the required 2 months so you can apply for a year extension at the immigration office for 1900baht before the 90 days runs out. You'll get a 30 day under consideration stamp and go back when that runs out to get the year inked into your passport.
This is the link for the eVisa system (if you're applying before you go back make sure you say you hold a UK passport and your permanent residence is in the UK or the system won't let you apply online)
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