What paperwork do I need to marry my Thai fiancé and how does the visa process work?

Go to the website of the thai consulate in London and read the requirements to come in on a 60 day tourist visa.

Once you're here you'll get stamped in for 60 days and you can extend that ONCE for 30 more days at the immigration office

That should give you enough time to get the freedom of affirmation to marry document from the UK consulate in bangkok, take it to a translator get it translated into thai, then take it to the ministry of foreign affairs office here to get it certified so you can show up at any Amphur (thai city hall) with your thai significant other and register the marriage.

Then in order to get a "marriage visa" you'd transfer 400K baht into a thai bank account in your name only and go to your immigration office when you have 15 days or more left on your current stamp. You pay 2000baht and then come back 2 weeks later and get the Non-O visa and a 90 day stamp inked into your passport.

Once you did all that you wait until the 400K baht money has been in your account for 2 months and go back and apply for a year extension based on marriage for 1900baht.

And that's how it's done 😛 🙂