The relevant body to contact in order to obtain a database for making structured lists is the Public Monuments and Sculpture Association (PMSA), who already have a database online in the form of the National Recording Project (NRP). Details are
here. Unfortunately this does not cover the entire UK, only about 70% of it. I know of three further online databases which cover areas not in the NRP:
Sussex,
Norfolk and Suffolk and
Sheffield (though this last one is not, to my mind, very good). UK involvement in the WLPA would presumably be dependent on the PMSA being willing to give us a copy of their database to create the necessary lists in time for May.
I am on good terms with Robin Owain, the Wales Manager of Wikimedia UK so I could contact him next in order to set the ball rolling. Is it best for the local chapter to contact the relevant institutions?