(1)The grant of a patent of addition shall not be refused, and a patent granted as a patent of addition shall not be revoked or invalidated, on the ground only that the invention claimed in the complete specification does not involve any inventive step having regard to any publication or use of--

(a) the main invention described in the complete specification relating thereto; or

(b) any improvement in or modification of the main invention described in the complete specification of a patent of addition to the patent for the main invention or of an application for such a patent of addition,

and the validity of a patent of addition shall not be questioned on the ground that the invention ought to have been the subject of an independent patent.

(2) For the removal of doubts it is hereby declared that in determining the novelty of the invention claimed in the complete specification filed in pursuance of an application for a patent of addition regard shall be had also to the complete specification in which the main invention is described.