Liability for costs
38.6—(1) Unless the court orders otherwise, a claimant who discontinues is liable for the costs which a defendant against whom he discontinues incurred on or before the date on which notice of discontinuance was served on him.
(2) If proceedings are only partly discontinued—
(a)the claimant is liable under paragraph (1) for costs relating only to the part of the proceedings which he is discontinuing; and
(b)unless the court orders otherwise, the costs which the claimant is liable to pay must not be assessed until the conclusion of the rest of the proceedings.
(3) This rule does not apply to claims allocated to the small claims track.
(Rule 44.12 provides for the basis of assessment where right to costs arises on discontinuance)