18.— (1) The parties to an arbitration agreement may agree on the arbitral tribunal’s powers regarding the award of interest.

(2) Unless otherwise agreed by the parties, the arbitral tribunal may award simple or compound interest from the dates, at the rates and with the rests that it considers fair and reasonable—

(a) on all or part of any amount awarded by the arbitral tribunal, in respect of any period up to the date of the award, or

(b) on all or part of any amount claimed in the arbitration and outstanding at the commencement of the arbitration but paid before the award was made, in respect of any period up to the date of payment.

(3) Unless otherwise agreed by the parties, the arbitral tribunal may award simple or compound interest from the date of the award (or any later date) until payment, at the rates and with the rests that it considers fair and reasonable, on the outstanding amount of any award (including any award of interest under subsection (2) and any award of costs).

(4) References in this section to an amount awarded by the arbitral tribunal include an amount payable in consequence of a declaratory award by the arbitral tribunal.

(5) This section is without prejudice to any other power of the arbitral tribunal to award interest.