PART IV
GENERAL RULES AS TO CRIMINAL RESPONSIBILITY
Mistake of fact
10. A person who does or omits to do an act under an honest and reasonable, but mistaken, belief in the existence of any state of things is not criminally responsible for the act or omission to any greater extent than if the real state of things had been such as he believed to exist.
The operation of this rule may be excluded by the express or implied provisions of the law relating to the subject.
Mistake of fact - national proceedings
EDIT.