Advice needed please - overseas adoption

[frumpet]

I have a freind who lives in Thailand , he is married to a Thai woman . They have three children , a son who isn't biologically my friends and two daughters . The two daughters have British or dual passports , the son having been born in Thailand only has a Thai passport . My Friend adopted the boy officially when he married the woman , mainly to protect him if anything happened to the woman . This adoption is recognised by the Thai goverment .
The problem is my friend is upset that his daughters have british passports but the boy doesn't and wondered if there was any way of making the adoption official in the UK , that would mean he was entitled to one . Basically he is very keen that all his children are equal in these terms .
I just wondered if anyone knew if there was any way of doing this

sorry its a bit long !

I don't think that Thailand is a convention country so adoptions in the Thailand are not legal in the UK (I need to double check that). I'll see what I can find out - I'm assuming they have no immediate plans to come back to the UK because the easiest route is to readopt in the UK when his son would get citizenship automatically.

Children adopted abroad by parents who are British citizens ? section 3(1) application

British citizen
This page explains how a child adopted abroad by parents who are British citizens can meet the requirements to be registered as a British citizen.

Applications for registration will be considered at our discretion under section 3(1) of the British Nationality Act 1981 if:

the adoption took place in a territory named in the Adoption (Designation of Overseas Adoptions) Order 1973; and
at least one of the adoptive parents is a British citizen otherwise than by descent; and
both adoptive parents have given their formal consent to the registration. There may be cases when it is not necessary for both parents to give consent. These cases are detailed on the completing the application form page; and
if the child is aged 10 or over they are of good character; and
we are satisfied that the relevant adoption laws have been followed in both the country where the adoption took place and the country where the child and parents will be living; and
we are satisfied that the adoption was not arranged simply to allow the child's entry into the United Kingdom.
Before making an application, you should make sure the child meets as many of the criteria above as possible and provide all the evidence you have to support the child's claim. Full details of the evidence we require can be found on the supporting documents page.

No i dont think thailand is a convention country unfortunately . They have been married for 11 years , Thailand is their home and they have no plans to return to the UK to live permanently at this stage .