It hasn't changed. If you're British by Descent you cannot pass on your citizenship to children born abroad. However, there are exceptions so definitely worth pursuing.
Your daughter is British by Descent so cannot pass on her British citizenship to her daughter, if she too was born in Thailand. Technically, anyway, but there may be a way round it if you consult a specialist.
Paying for sexual services with an underage provider is illegal. It makes no difference whether they were 'barfined' from a bar, or whether they showed fake ID.
Possibly a more up-to-date link here:
https://www.gov.uk/get-document-legalised/apply-for-legalisation
Definitely easier to do if you're in the UK, but apparently can now be done online.
On the contrary, many of us have had to do exactly what the OP is asking. This is how Forums work. All the Embassy will do (if they respond at all) is refer him to the website I've already listed.
All the UK Embassy will do is refer you to the gov.uk website. All the answers are there, although the OP has received good advice here, which is what the Forum is for.
https://www.gov.uk/get-document-legalised/apply-for-legalisation