I am married to a Thai national in UK but did not have time to legalize the marriage to the embassy.

Where can I do it in BKK and what is the procedure ?

The procedure is to have the wedding certificate certified by the British embassy (ask them what they require for that). Next you have it translated into Thai and when that is done you have it certified by the Thai Foreign Ministry.

When this is done you make copies and/or scans of these documents for future use. (Immigration might ask for them)

Now you can have the marriage registered at any amphur in Thailand. Of this you will receive a khor rhor 22 form that confirms your foreign marriage and is required by immigration for an extension based on marriage but also otherwise proofs your foreign marriage.

At the embassy you will do a declaration that the marriage certificate is authentic. Then you have it and the marriage certificate translated to Thai and have the translation certified at the MFA. The translation service can do the certification for you for a small additional fee.

Then as said you go the local Amphoe and register your marriage. They will update your wife's house book and do a new ID card with her married name on it if she wants it that way.

Would I be right to assume all of this procedure is required for the Thai wife to change her name to her farang husband's? (If they were married out of Thailand). I mean, can she change the name without the bit about 'legalizing'?

Would I be right to assume all of this procedure is required for the Thai wife to change her name to her farang husband's? (If they were married out of Thailand). I mean, can she change the name without the bit about 'legalizing'?

It is not just to change her name. In fact that is no even required. A women has the choice of keeping her maiden name and be shown as Miss on her ID card.

If is to register the marriage and obtain a Kor Ror 22. Until this is done the marriage is not officially recognized here.

As said your marriage is fully legal. But to extend your stay for marriage using immigration would require it be recorded in Thailand at the District Office and at that time a change of name can be made or not. It is easy for Thai to change name in any case - but actually most prefer to be known with Thai name in Thailand to avoid the higher price discounts a foreign name often attracts. In the past it was an issue as land ownership would not be recorded if having a foreign name but there is a work around for that now so only requires an extra paper and that funds were yours alone for purchase statement.

My wife had no choice when we got married because it was before the law was changed to comply with the 97 constitution.

She has never had a problem because she has my name.