The regulatory changes in relation to ports introduced from 1 April 2005 concerned the valuation basis on which the statutory designated port operators' occupations are assessed (moving from a “formula” to a “conventional” basis). They did not change the law regarding what should or should not be separately assessed, under which the present action is being taken.
Valuation officers have no discretion over the effective date from which alterations in assessment take place, which is prescribed by separate regulation of general application. The valuation officers are simply discharging their normal functions, so no impact assessment has been undertaken by or on behalf of HM Treasury.