7. The extent to which, in the opinion of the Common Council, of each relevant precepting authority and (in a relevant case) of the National Rivers Authority, any difference between the amount mentioned in paragraph 4 and the amount mentioned in paragraph 6 for the body is attributable to—
(a)inflation,
(b)differences in the grants received or expected to be received with respect to the year,
(c)changes in the quantity or quality of services provided by the body, and
(d)differences in the income received or expected to be received by way of fees and other charges for its services with respect to the year.