10. (1) This regulation applies where a relevant supplier is notified by a customer—
(a)that the customer considers that an appropriate meter is or may have been operating outside the margins of error; or
(b)that circumstances exist which a relevant supplier might reasonably expect to have been caused by the meter operating outside the margins of error.
(2) Where this regulation and paragraph (3) apply, and the relevant supplier fails within the prescribed period from the applicable date to offer to visit the customer’s premises to investigate the matter during a specified time the relevant supplier shall, except in any of the circumstances described in paragraph (5), pay to the customer the prescribed sum.
(3) This paragraph applies where the relevant supplier is reasonably satisfied that he is unable to provide an explanation to the customer of the probable reason for the matters notified under paragraph (1) without visiting the customer’s premises.
(4) Where this regulation applies and the relevant supplier—
(a)where paragraph (3) applies, fails to visit the customer’s premises during the specified time he shall pay to the customer the prescribed sum; or
(b)where paragraph (3) does not apply, fails to dispatch to the customer an explanation of the probable reason for the matter notified under paragraph (1) within the prescribed period from the receipt of the notification he shall pay to the customer the prescribed sum;
except in either case in any of the circumstances described in paragraph (5).
(5) The circumstances described in this paragraph are each of the circumstances described in regulation 17 provided that, in relation to paragraph (6) of that regulation, the relevant supplier gave the customer not less than one working day’s prior warning (whether or not in writing) that he would be unable to visit during the specified time or the circumstances referred to in that paragraph occurred at a time when it was not reasonably practicable to give such a warning.