Where the operator of an authorised landfill site, in calculating the taxable weight of the material in a taxable disposal—
(a)applies a discount without having approval under section 21 to do so, or
(b)applies a discount which is greater than the discount approved under section 21,
the operator is liable to a penalty not exceeding £500 in respect of each taxable disposal to which a discount is applied in either of those ways.