The answer is obvious

Lord Leveson, as a sitting judge, feels he is too grand to be grilled by the Commons about his multi-million-pound inquiry into minor hacking by Her Majesty’s Press (trivial compared to what the legal trade gets up to). Lord Hutton (Iraq whitewash) appeared before the Commons when he was retired. So the solution to the Leveson problem would appear to be to fire him. Then he won’t be a sitting judge any more and he won’t have a valid excuse for failing to explain himself.