Yes, I am going through this process ready for my forthcoming extension, a right ball ache. A UK issued marriage certificate is accepted in almost all countries but for some reason not Thailand, a complete nonsense in my opinion. I have also had to have my passport translated which is another nonsense!
I believe also that I have to download a form which of course I can do but then it's got to be posted to UK. I can't see that having somebody in the UK, which I do have , would help, or am I being thick!