39.— (1) Before the end of each month, the Minister shall notify the Agency of the Minister’s assessment of the volume of each category of petroleum products appearing to have been relevantly disposed of in the preceding month by each oil company and oil consumer liable to pay the levy.

(2) The volume assessment is to be based on—

(a) the information supplied by the oil company or oil consumer in accordance with the regulations relating to returns, or

(b) if that information has not been supplied or if the Minister has reason to believe that information so supplied is inaccurate or incomplete in any material respect, such estimates as appear to the Minister to be reasonable having regard to any other available information.