(1) Part 2.3 (Notice of intention to respond and defence) applies, with necessary changes, to a proceeding started by a third-party notice as if—
(a) the proceeding were a proceeding started by an originating process; and
(b) the third-party notice were the originating claim in the proceeding; and
(c) the defendant were a plaintiff and the third party were a defendant in the proceeding.
(2) The third party may, in the defence to the third-party notice, deny a plaintiff's claims against a defendant and claim a matter showing a plaintiff's claim against a defendant is not maintainable.