Depending on the relationship you have with the Thai lady will decide the type of UK travel visa that is likely to be issued by the department of immigration.
Thai lady, girlfriend, wife
If the Thai lady is in a sexual relationship with you and could be classed as your partner, girlfriend or wife, then a UK tourist visa or UK Marriage – settlement visa would be of the type of visas available to allow travel to the UK
For a Thai lady at school, college or university, a UK student visa would be the best option. For a Thai lady setting up or running a business within the British isles, a UK Business visa would be the best visa.
No matter what the circumstance a visa for a Thai lady to the UK is available. The department of immigration will need to be satisfied that the visa application is true and honest and importantly that the Thai lady will return to Thailand prior to the UK visa expiring.
The UK immigration department has the right to issue or refuse UK visas. There is an avenue for complaint if you feel the decision is incorrect and unjust, though dealing with any large organisation or government department will be difficult to tackle.
Getting a Thai lady to the UK is possible
Getting a Thai lady to the UK is possible, first find the visa most suitable for her situation, and then prepare the evidence that will be required to back up the visa application. Ensure that the Thai lady is prepared for an interview at the British embassy. The visa officer can request an interview if they feel the application requires further investigation.