2 sets of laws governing one country is a recipe for chaos.
It's a nonsensical headline. There's no change in the law. The Law Society (the lawyers' professional body) can't make or change laws. All they're doing is providing their members with an off-the-shelf tool for drawing up wills in a way that certain clients want (in this case certain Muslims). Such off-the-shelf proformas already exist for all the conventional forms of will. Using them simply saves the lawyer time, and therefore the client money. Has no implications for the law itself.