It will take time. First, you need to make an online appointment with the British Embassy to make a certified copy of your passport:
https://book-consular-appointment.service.gov.uk/TimeSelection?location=53&service=8
The nearest appointments are about 1 week away. The service costs £25.
Alternatively you can send your passport to them. Details here:
https://www.gov.uk/guidance/notarial-and-documentary-services-guide-for-thailand#certified-copy-of-a-british-passport
Once you have the document you need from the British Embassy you will need to drop it off at a reputable translation company, along with a copy of your marriage certificate. The translation company will need a copy of your marriage certificate to get the exact translation required.
It's also likely the translation company will require a copy of your passport, so do take that to the translation shop aswell.
The translation shop will make the translation and then take all required documents to the Ministry of Foreign Affairs for legalisation. The translation shop will need to book an appointment at the MFA. Again, there is a waiting time to get a slot. Once at the MFA the legalisation will also take time.
I believe there is an express option with the MFA if required.
I am currently having a document translated and legalised.