If a person is entered in an authority's register as subject in a chargeable financial year to a collective community charge of the authority, he shall be liable to pay to the authority an amount in respect of the charge as it has effect for the year.
The amount shall be found by deducting amount B from amount A.
Amount A is the aggregate of the amounts payable (and whether or not paid) to the person by way of contribution to the amount he is liable to pay to the authority in respect of the charge as it has effect for the year.
Amount B is an amount equal to the relevant proportion of amount A; and the relevant proportion is 5 per cent. or such other proportion as may be prescribed by the Secretary of State by order.