Do I need to authenticate my British passport at the British Embassy for a Type-O visa application in Thailand?

I understand you like to keep this post open but than keep to the facts. You had a work permit and Extension of Stay from the one stop service of the BOI. You went to cancel this at the normal Immigration Office, as you posted and discussed this a few days ago. You got the advice to visit the one stop service center of the BOI again to deal with that as it normally is handled that way. Now you claim about passport problems, but you did not even visit the Immigration Office. As I mentioned before, you have to go in person to apply for the Non Immigrant O visa based on marriage OR the 60 days Extension of Stay based on marriage. Not sending your wife with your passport.

I guess because your marriage certificate is not in Thai you will need your passport and/or married certificate translated into Thai and legalized. When getting married in Thailand you same need your passport translated and legalized. Maybe your Embassy will do both translation and legalization. Maybe it also needs to be legalized by the Ministry of Foreign Affairs. Those of us staying for long have tried the route back and forth Embassy and Ministry again and again. The Ministry has a translation service which is acceptable by the Ministry. They do it while you wait.

To apply for a visa you need to go in person. Your wife can not apply, now I understand the confusion in handling with passport. Address registration or even the 90 day report is no problem to sent another with your passport. But not for applications for Visa or Extension of Stay.

Ok in that case my idea of why they are looking to get the passport verified is irrelevant if you actually applied directly in the UK

Can I ask where you obtained the passport?

They need to prove the passport does not fake that why I have to go UK embassy to do this..

I not understand. You have an British passport that is good enough to make an address registration but not good enough to apply for a visa?

Never heard of this one, easier to go to Savanaket