See how converting a civil partnership works. This is not very common however you can convert a civil partnership to a marriage while in the UK. This is one of the processes you can do while in the UK. There are requirements to achieve this and you would be best served to speak to an attorney and take legal advice before you embark on the process.
Consider converting a civil partnership into a marriage. There are other options such as a UK spouse visa for a Thai national as well as a UK fiancée visa from Thailand.
If England and in Wales this can be done at a church or at a register office. The Home Office keeps a list of premises that have been approved for civil marriages and civil partnerships in England and Wales. They will now give you a marriage certificate dated on when the civil partnership was formed. The fees for this is normally just under £100.
The process starts with signing a ‘conversion into marriage’ declaration. This is done at the local register office however you will also need to provide a civil partnership certificate and your ID document. They will normally tell you what type of ID they will accept.
If you already had a civil partnership in the UK then you can convert this while abroad. They will then give you a marriage certificate based again on the date the civil partnership was formed. The British Embassy or Consulate will do this for you. This can however only be done in certain countries. These are:
You will need to provide your passport as well as that of your civil partner and also provide proof that you are a resident of the country you are in. You will also need the original civil partnership certificate which was issued to you.
Firstly as you will note that this cannot be done in Thailand. Speak to an immigration lawyer in Thailand about your options. There is a UK fiancée visa for a Thai national as well as a UK spouse visa for a Thai. Speak to a lawyer about other options and also about family law in Thailand and in the UK if there are children involved in the move back to the UK. There is also the issue of property in Thailand as the UK as well a prenuptial agreements to consider. Finally with sound legal advice you cannot go wrong converting a civil partnership.