What visa should I apply for as a UK citizen planning to marry my Thai girlfriend and stay in Thailand?

You need to apply for the Non Imm O visa. It's both the marriage visa and the visa for being 50 and over(commonly called the retirement visa). You'll need this visa to open a bank account and to apply for a yearly extension of stay.

You need to look what you need for o-visa marriage,get bank as soon as possible it needs to be in the account for 2months for the first time,bangkok bank is best to try first they will ask you to take insurance as a way to make money but it now hard to get now ,so anymean is best ,in the o- visa application it ask you for how much money in the uk thinking it's about £10,000 uk,800,000 thai bauts bank account

Just a thought you need ,310 days from divorce to get married in Thailand, that caught me out the first time ,I got married in the first month of the o-visa, as I did not have the 800,000 buat for retirement visa, if you have ok that's great and do that o-visa its all online now ,and the photos copie are in j,pack mode ,don't know about it, but daughter did ,(picture have to much detail in it I think,it was to big to load )and when you do the o-visa do on pc or laptop phone will not show all the details on the page,I miss abit of it on the phone, you have to click on the sample passport in the application to download you bio passport details, read it carefully, I did it twice £60 a time ,marrying a thai person yes,

Since you will need a bank account and without a long term visa it will be very difficult I would apply for a non o visa ( retirement i.e. over 50) through the London embassy now before you go. This should give you 90 days in thailand and give you the best chance to open a bank account when you arrive. You can then deposit the required funds to get your extension inside thailand. With a non O visa you can then just organise your departure flight and worry about your return flight when you are in thailand as this visa will be accepted for one way travel i.e. no return or onward travel required. This will give you the best chance to set yourself up when you arrive

To open a bank account you need to get a Non-O retirement Visa, do that for your April arrival and you'll get a 90 day entry stamp to get things set up. You can get a marriage Non-O further down the line or swap from a retirement Extension of Stay to a marriage Extension of Stay in the future.

Go for retirement

@Robert *******