anyonenobody; "Common sense would tell you that King's is not the best law school in the UK" Common sense is utterly unreliable as a source of data.
Besides which, common sense needs to be common to all; ask the question of UK law school rankings in a Barrow Shipyard and you'll get an odd look, if you're lucky. By contrast, the REF is compiled using the ranking provided by other legal academics; a more reliable source than any of us here.