Timatic requirements for British Citizen, resident in UK, leaving Indonesia:

Thailand - Destination Passport
Passport required.

Document Validity
British passports must be valid for the period of intended stay.

Contrast Singapore which has a 6 month rule

Singapore - Destination Passport
Passport required.

Document Validity
Passports and other documents accepted for entry must be valid for a minimum of 6 months from the arrival date.

Cathay and their outstations should follow Timatic - CX doesn't have a 6 month hard rule like Airasia (https://support.airasia.com/s/articl...language=en_GB ?)