It is important that if you plan on getting married in the UK to your Thai girlfriend, then you need to apply for a Fiancee visa. Without the visa, it will be impossible to marry at any registry office.
Provisional wedding booking from a UK registry office
In the past, to help with the fiancee visa application, couples have supplied a provisional wedding booking from a UK registry office to demonstrate that marriage is planned. This evidence is now almost impossible to provide as from February 2005, the marriages and civil partnership office in the UK introduced new guidelines stating that a provisional wedding could only booked after the fiancée visa is in the Thai girlfriends passport.
Making a Marriage booking
A notice of marriage is only valid for one year in the UK. You can make a provisional marriage booking by telephone or in person at a register office.
It is important to remember that your notice of marriage must be given to the Superintendent Registrar of the district in which you reside regardless of where the marriage is to take place.
When giving notice of marriage you will need to provide evidence of your identity, nationality and visa required.
So if your Thai girlfriend hasn’t a valid fiancée visa in her Thai passport, then the notice of marriage will not be provided.