31Registration to be prima facie evidence of validity.

(1) In all legal proceedings relating to a trade mark registered under this Act (including applications under section 57), the original registration of the trade mark and of all subsequent assignments and transmissions of the trade mark shall be prima facie evidence of the validity thereof.
(2) In all legal proceedings as aforesaid a registered trade mark shall not be held to be invalid on the ground that it was not a registrable trade mark under section 9 except upon evidence of distinctiveness and that such evidence was not submitted to the Registrar before registration, if it is proved that the trade mark had been so used by the registered proprietor or his predecessor in title as to have become distinctive at the date of registration.