(1) A concurrent wrongdoer who is sued for damages or for contribution and who wishes to make a claim for contribution under this Part -

(a) shall not, if the person from whom he proposes to claim contribution is already a party to the action, be entitled to claim contribution except by a claim made in the said action, whether before or after judgment in the action; and

(b) shall, if the said person is not already a party to the action, serve a third-party notice upon such person as soon as is reasonably possible and, having served such notice, he shall not be entitled to claim contribution except under the third-party procedure. If such third-party notice is not served as aforesaid, the court may in its discretion refuse to make an order for contribution against the person from whom contribution is claimed.

(2) The provisions of subsection (1) of this section shall not apply to any contribution claim where the parties to the claim are precluded by agreement or otherwise from disputing any earlier determination by a court of the amount of the injured person's damages and the proportion in which contribution should be made.