12. A supplier must—
(a)establish a methodology setting out the basis on which it will make the determinations under regulation 11(1);
(b)keep the methodology under review and update it if appropriate, having regard in particular to—
(i)any change in the basis or terms on which it enters or offers to enter into supply contracts;
(ii)any determination of the Secretary of State in respect of the categorisation of the supplier’s supply contracts under Chapter 4 of Part 5;
(c)maintain, in respect of each supply contract, the data necessary to make the determinations under regulation 11(1) in accordance with the methodology;
(d)ensure that it has in place reliable systems and procedures to apply the methodology.