The issue that is trying to be solved is the self limiting of selection pools. What DEI in the UK attempts to do is to increase the number of people a selection is made from. It acknowledges that often self limiting selection pools not based on merit exist and attempts to remove those limits. An example I have used in the past is as mundane as to where you place your adverts for a particular role, that can limit the size of the pool not based on merit or qualifications but who reads (as an example) the magazine you have "always" placed your adverts in.
