A company called VFS now handles all UK Visa applications and there website is at
http://www.ukvac-th.com/
There even the possibility to "track" an application online !! Shame my GF sent me the wrong numbers but insisted they were correct, I was quite looking forward to seeing how that part worked.
I have recently heard of 2 people getting their GF's visa by using the Chiang Mai branch of the UK Embassy. One of them was a mate of mine who said that compared to Bangkok, where the application was refused, CM was a doddle. Perhaps this is a better way to apply, especially if your GF lives in the north.