There are a number of options when it comes to the UK visa. If you wish to visit the UK as a tourist or to visit friends then you can apply for a UK visitors visa. Note that you cannot take your Thai fiancee to the UK on this visa to get married. You have to apply for the correct British visa in Thailand. The other options are a UK Fiancee visa which is very common in Thailand and the UK spouse visa for your Thai wife once you have registered your marriage in Thailand.
The following are the options for the UK visa in Thailand. Note that all the visa processing is done in Bangkok and your fiancee or spouse would have to travel to Bangkok for an interview at the British Embassy when the time comes. Visa denials are not uncommon in Thailand and if your Thai fiancee has been denied a UK visa then speak to us about the visa denial today.