Business Rate Supplements Bill

I am still a little puzzled. I understand that the reliefs are captured by the formulae in Clause 13, but then why is Clause 15(1) necessary? It says that a levying authority may apply such reliefs as it thinks appropriate. Does that mean that it could apply greater reliefs than those which will already have been taken into account in reaching the cash amount under Clause 13? Does it mean that it can make up its own local reliefs? I remain a little puzzled. Can the noble Baroness help?