I did the whole process a week ago thought initially I would do everything myself. British embassy you need to do by yourself book online after downloading your documents. Embassy took 15 minutes then to mofa ( went to wrong address) arrived mofa greeted by translation agents gave 2600 baht for translation ready for collection after mofa 4 days later.
Tried getting appointment @ bang lamung waited time phoned translation company another 5000 went laksi married 30 mins after arrival total 8 days and about 8000 baht and £75 to embassy
//Edit by Maestro: For "mofa", read MFA (Ministry of Foreign Affairs)