If you're getting married in the UK, get the marriage certificate legalised by the UK Legalisation Office in Milton Keynes, then certified by the Thai Embassy in London, before you come to Thailand.
For UK citizens there is only an ETD which is sometimes referred to as an Emergency Passport - valid for 1 year, but there must be a journey itinerised : "The emergency passport can be used to make a single or return journey to the UK or another country of residence, via a maximum of five transit countries.
The emergency passport is issued with a validity which is limited to the shortest time appropriate to the holder’s travel requirements whilst taking account of the transit and destination country requirements (for example, many countries require travel documents to have a minimum validity of six months)."
"You will be asked to provide an itinerary for your journey".
I was categorically told by the UK Consulate that an ETD could not be used for Immigration purposes - only for travelling "home".
Really? We made one for ours back in November. Maybe it's changed now, but it was a vast improvement. Processed our whole family's extensions within an hour of the appointment.