Name change after marriage UK / Belgium

Although my experience isn't identical to yours, it does have many similarities so I hope it will be helpful. My wife is Thai and we married in Thailand. Following the marriage the registrar issued a certificate of surname change (more or less equivalent to a deed poll) because my wife wanted to adopt my surname, and she used this certificate within Thailand to have things like the name on her bank account changed. It also supported her application for a new Thai passport in her married name.

In the UK, whilst there is no automatic assumption that a woman will take her husband's surname on marriage, a marriage certificate can be used as evidence of your new name; a deed poll doesn't seem to be a legal necessity. I've found a couple of websites confirming this, and I have no doubt there are others.

https://www.deedpoll.org.uk/a-womans-ri … -marriage/

https://www.netlawman.co.uk/ia/change-name-marry

You can even apply for a British passport by submitting your original marriage certificate. You may find, however (and you would probably know whether this is the case), that in Belgium a marriage certificate is not by itself sufficient evidence to support an application for a replacement Belgian passport, especially since your marriage certificate is in English, and that you do indeed need a deed poll.

I cannot comment on what would be expected in Belgium, but logically I would have thought that once you have a new passport with your husband's surname, that would be all the evidence you need to prove the name change.