okthen, uk Govt website -
After you get married
Your marriage will be recognised in the UK if both of the following apply:
you followed the correct process in the country where you got married
it would be allowed under UK law
You may want to consider translating your Thai marriage certificate into English and getting it legalised by the Ministry of Foreign Affairs in Thailand or the Royal Thai Embassy in London, especially if you wish to use it outside of Thailand.
There is no requirement or facility to register your marriage in the UK. You will need to keep a copy of your local Thai marriage certificate as evidence of your marriage.
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