I am based in the Republic of Ireland and only get a small number of orders from the UK.
I decided that, at the moment, I don’t want to sell to the UK as I don’t want to have to register for UK Vat and submit returns.
I simply deleted the UK from my shipping to list, in manage shipping profiles, in shipping and deliveries.
I then tested a sample order with a UK address and got the notice at shipping “this store does not ship to your country. Contact the store owner”.
Hope that is helpful.
For me, it does create a problem with customers from Northern Ireland as it is part of the UK but for the Irish post office, it is the same rate as the Republic of Ireland. BUT that is for another day’s discussion.