For the purposes of this Act, any new claim made in the course of any action shall be deemed to be a separate action and to have been commenced—
(a) in the case of a new claim made in or by way of third party proceedings, on the date on which those proceedings were commenced; and
(b) in the case of any other new claim, on the same date as the original action.
In this section a new claim means any claim by way of set-off or counterclaim, and any claim involving either—
(a) the addition or substitution of a new cause of action; or
(b) the addition or substitution of a new party;
and "third party proceedings" means any proceedings brought in the course of any action by any party to the action against a person not previously a party to the action, other than proceedings brought by joining any such person as defendant to any claim already made in the original action by the party bringing the proceedings.
Rules of court may provide for allowing a new claim to which subsection (3) above applies to be made as there mentioned, but only if the conditions specified in subsection (5) below are satisfied, and subject to any further restrictions the rules may impose.
The conditions referred to in subsection (4) above are the following—
(a) in the case of a claim involving a new cause of action, if the new cause of action arises out of the same facts or substantially the same facts as are already in issue on any claim previously made in the original action; and
(b) in the case of a claim involving a new party, if the addition or substitution of the new party is necessary for the determination of the original action.
The addition or substitution of a new party shall not be regarded for the purposes of subsection (5)(b) above as necessary for the determination of the original action unless either—
(a) the new party is substituted for a party whose name was given in any claim made in the original action in mistake for the new party's name; or
(b) any claim already made in the original action cannot be maintained by or against an existing party unless the new party is joined or substituted as plaintiff or defendant in that action.
Subsections (3) to (7) above shall apply in relation to a new claim made in the course of third party proceedings as if those proceedings were the original action, and subject to such other modifications as may be prescribed by rules of court in any case or class of case.
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