Any visa application for a visa to the UK for a Thai GF must be made at the British embassy Bangkok. The Thai GF will have to demonstrate at the time of the visa application that she has reason to return to the UK at the end of the visa. If the Thai GF has a professional job, savings, land or a home this goes part way to demonstrate this.
Requirements for Holiday Visa Thai GF
The Thai GF will have to show that they have sufficient funds for the UK holiday and return flights to and from Thailand. The Thai GF if being sponsored by a UK boyfriend will have to prove there is a real relationship between the Thai GF and the UK sponsor that they keep in touch regular.
All visa documents must be provided in English only. Before the Holiday visa for a Thai GF is issued, an interview will take place with your Thai GF.
The information only goes part way to what is required at the time of the Holiday visa for a Thai GF.