No one knows unfortunately, well no one that knows is allowed to share that with us.
I would say it's imminent though as they have or are just about to release the full version on the S21. The beta has been open for the Fold and Flip for at least a month in other regions and you can install it manually if you want to (search on XDA). Your devices must have a CSC code of BTU though for you to be able to install it manually or for you to receive the Beta Banner on here. You can change your CSC if you are a little technical and can follow instructions.
Saying all that and based on where they are with the s21 beta, I would not be surprised if they don't release the Fold beta in the UK and just do a full release in a month or so.