Can I bring 800,000 Baht in cash to open a Thai bank account?

Paul, the simple answer is yes, you can move cash, up to you whether you declare it or not. The problem is generally only with 3rd world countries who try to restrict money being taken out... hence filling in the form declaring what you are bringing in to Thailand is best... it is both proof of foreign funds and allows you to take the money back out of Thailand should the need arise.

This said, there are reasonably cost effective ways to send funds safely that are workable.

Equally, using an agent for the initial set-up of accounts and visas is very hassle free with zero headaches, covering the first 15 months, albeit frowned upon by some.

Thereafter you may renew yourself.

That amount of cash will raise flags at every stage and is a security risk. You're better off losing a few £ on the transfer through a bank.

Lloyds bank only charged me £9.90 for international fund transfer last year.

Not sure of UK banks. But Irish banks charge around €20 for transfer of €20K euro. Not sure what rate they offer

Try wise transfer funds but you will need a thai bank account

Taking cash over instead of using a card will save you a lot of money, but your only allowed to take £10k without declaring it, it’s hard to open a Thai bank account now. If you’re thinking of buying a condo or something it’s best to transfer your money through wise etc. But make sure you declare your buying property, as it’ll go through as a foreign transaction.

I think you can only take £10k out of Uk

You can bring your cash just dont fordet to declarate it on the Thai custom. And keep that declaration to show in Thai bank for open acc and exchenge you currency to confirm your money came with you outside Thailand

If you are trying to live in Thailand, then you will need to apply for the non-O retirement visa before you travel to Thailand. Otherwise you will not be able to open a bank account, and even if you could it would not help you if you didn't already have the visa, because in order to apply for the visa in Thailand you must show that the money was TRANSFERRED from overseas, not brought in as cash. So apply for the non-O visa, travel to Thailand. Use the visa to open a bank account and then deposit your money after you exchange it. Then after the money has been in your account for 2 full months you can apply for the 1-year extension based on retirement.