Where electricity generated from eligible renewable sources has been sold by the operator of the generating station to an electricity supplier (or to a Northern Ireland supplier, in the case of a generating station which may lawfully be supplied with electricity by a Northern Ireland supplier) and is then purchased from the electricity supplier (or, in the case as aforesaid, from the Northern Ireland supplier) and consumed by the operator of the generating station, such electricity shall be regarded as having been supplied by an electricity supplier (or, as the case may be, by a Northern Ireland supplier) to a customer.