There is still much confusion in Thailand when it comes to applying for your child’s first UK British passport and you must remember that when applying for your child’s first UK British passport you do not send the application to Hong Kong it must be applied for at the British Embassy Bangkok.
The most common mistakes we see are that the British father needs his original birth certificate and it must be the birth certificate that has your mother and fathers name on so they can see the origin of your parents “must be an original” not a copy.
All documents sent to the British Embassy in Bangkok must be originals complete with photocopies and all the Thai documents must be translated in to English, you must also make sure that your child’s name is spelled correct on the translations as there is numerous ways a Thai translator can spell an English name it sounds stupid but in most cases you are better giving them the name written down how you wish it to be spelled.
We apply at Key Visa for many first UK British passports for children and we have a hassle free service including application forms, translations, submitting the application etc at a reasonable cost,
Please read http://www.keyvisathailand.com/our-services/british-passport-for-thai-child/ and it also gives you the documents required in an easy read list.