I'm already married but for the sake of this question, I think I'd have to go to Gretna Green.

You can't ''just get married'' in the UK. You have to go to the local registry office, put in an application for a licence and confirm you're not actually related to your intended.

If that goes through, then there are only certain approved venues where you can wed. In the UK, you cannot get married at home. It has to be a licenced venue.