15. An authority may require an operator to allow officers, servants or agents of that authority to have access with reasonable frequency to (including the right to travel free of charge on) the vehicles of the operator on which mandatory travel concessions are provided for the purpose of—
(a)surveying or counting or estimating the number of passengers (whether generally or of any particular description) and the fares values attributable to those passengers; and
(b)obtaining information on other matters relating to the journeys made by passengers who are entitled to be provided with mandatory travel concessions and necessary to the calculation by the authority of reimbursement payments.