541. Putting validity in issue.

The validity of a patent1 may only2 be put in issue3:


    (1)     by way of defence in infringement proceedings4 or proceedings5 for infringement of rights conferred by the publication of an application6;


    (2)     in proceedings7 in respect of an actionable threat8;


    (3)     in proceedings in which a declaration of non-infringement9 is sought10;


    (4)     in revocation proceedings11 before the court12 or the comptroller13;


    (5)     in proceedings14 on a dispute as to Crown use15.

No determination may, however, be made in any such proceedings on the validity of a patent which any person puts in issue on the ground of lack of