6.—(1) Save as provided in regulation 7, in a case where works are initiated by a person other than an authority in its capacity as such or an undertaker and for the purposes of that person, and, because of those works, measures need to be taken in respect of apparatus—
(a)if the authority takes those measures, the undertaker shall pay to the authority a sum equal to 18 per cent of the allowable costs incurred by the authority in taking those measures;
(b)if the undertaker takes those measures, the authority shall pay to the undertaker a sum equal to the allowable costs incurred by the undertaker in taking those measures, provided that the authority shall pay only 82 per cent of the said allowable costs if the authority pays to the undertaker a sum equal to 75 per cent of the estimate of the said 82 per cent pursuant to sub-paragraph (a) of regulation 9.
(2) For the purposes of this regulation, in calculating the cost of taking measures, there shall be taken into account in favour of the undertaker any sum which is recoverable from the person for whose purposes the works are done, irrespective of whether or not such a sum is actually recovered from that person, or any sum which would have been recoverable if the person for whose purposes the works are done were not the authority.