(1) A party may make an offer to another party which is expressed to be “without prejudice” and in which the offeror reserves the right to make the terms of the offer known to the court after judgment is given with regard to —
(a) the allocation of the costs of the proceedings; and
(b) (in the case of an offer by the claimant) the question of interest on damages.
(2) The offer may relate to the whole of the proceedings or to part of them or to any issue that arises in them.