PART XITIME OF SUPPLY AND TIME OF ACQUISITION
Royalties and similar paymentsI191
Where the whole amount of the consideration for a supply of services was not ascertainable at the time when the services were performed and subsequently the use of the benefit of those services by a person other than the supplier gives rise to any payment of consideration for that supply which is—
a
in whole or in part determined or payable periodically or from time to time or at the end of any period,
b
additional to the amount, if any, already payable for the supply, and
c
not a payment to which regulation 90 applies,
a further supply shall be treated as taking place each time that a payment in respect of the use of the benefit of those services is received by the supplier or a VAT invoice is issued by the supplier, whichever is the earlier.