A statutory public inquiry would enable interest groups to be given core participant status and access to important disclosure so as to bring their expertise to bear and make submissions. Potential contributors to the inquiry would be entitled to legal representation should they want it.
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I believe that the Met has shown in previous non-statutory inquiries that they cannot be expected to provide their full cooperation and candour voluntarily. A statutory public inquiry would bring the requisite powers to compel witnesses and gather relevant evidence.