Is it possible to get a British passport from the consulate here in Chiang Mai for a child born to British/Thai parents?

I have mainly read it be done from Bangkok.

If so, apart from the child's birth certificate, what else is needed?

You have to send away to Hong Kong.

The consulate here is very helpful, I recommend you go and see them.

You will need the forms, copy of the birth certificate and a certified translation. Plus photos, the UK govt relaxes the rules a bit for new borns but it can still be difficult to get an acceptable shot. The studio around the corner from the consulate does a good job and know the rules. The pictures then have to be certified by an appropriate person and countersigned in the form.I think you also have to include copies of the parents 'passports.

It takes about 6 weeks but is actually quite straightforward, at least it was for us for both our children.

The consulate will send away for you.

You need the British parent's full birth certificate (long version), both parents' passports (if available), marriage certificate (and translation if not in English) helpful if available and the child's birth certificate (and translation if not in English) hopefully with the British parent named as mother or father.

edit: and anything mentioned in the above post I forgot. The consulate are very helpful, as far as they are allowed to be.

Thanks for these helpful replies