You need to be very careful about the course you take in Thailand.
I am afraid that many (indeed most) do not train you to a standard that CTHA can accept for membership or insurance.
CTHA is having to arrange assessments for many who have trained in Thailand because the courses out there are often more "tourist" based and do not cover nearly enough A&P,basic massage, and sufficient case study work in Thai massage.
If you have full UK Massage qualifications it helps as you will have the basis
Do check with the office before signing up