What are the steps to apply for a Non-O visa as a British national married to a Thai citizen?

Okay, then you can do as

@Ja***

suggested and go to a thai consulate in a nearby country and get a year-long, multi-entry Non-Immigrant Type O visa based on marriage

The three thai consulates that do not require proof of funds to issue that visa are the ones in Ho Chi Minh City Vietnam, Savannakhet Lao, and Seoul South Korea.

You need the original marriage certificate (if you're married in thailand it's the one with the rose border around it).

You need copies of

-the front&back of the marriage certificate

-the front&back of your wifes thai i/d card

-her thai house book listing

-the data page of your passport

-your visa and entry stamp to what ever country you go to

If you use Ho Chi Minh City or Seoul, you need a letter from your wife asking them to issue you the visa.

Savannakhet takes thai baht a the consulate, HCMC takes US dollars, and Seoul takes Korean Won.

If you cannot meet the 400k goto HCMC

Are you able to meet the financial requirements of 400K baht in a thai bank account in your name only for 2 months prior to your application for the Non-O visa/extension based on marriage?

You're gonna hafta narrow that down some

What is your nationality?

What is the reason you're getting a Non-O visa?

Are you currently inside or outside of thailand?

Do you want to do it inside the country at the immigration office or get it form a thai consulate in another country?

Provide a little more information so people can help you