If the appellant entertained an honest though mistaken belief that the complainant was consenting to the acts of intercourse as they occurred, the necessary mens rea would not be present and the appellant would be entitled to an acquittal. An accused person who seeks to rely upon a defence of mistake of fact must, in order to succeed, establish that his mistake was reasonable as well as honest.
Dickson J. dissented on evidentiary issues related to this case specifically. Nonetheless, McIntyre J., for the majority, endorsed Dickson’s outline of when mistake of fact is available as a defence (p. 627).
Sansregret v. R.  1 S.C.R. 570
Sansregret went to his ex-girlfriend’s house in the middle of the night brandishing a knife. In order to diffuse the tense situation, his frightened girlfriend would consent to have sex with him. The trial judge found that the appellant honestly believed that the complainant was giving a free and genuine consent to intercourse. She found that the complainant, who knew the appellant, also believed in the honesty of his belief.
Was the mistake of fact defence available to the accused?
No. Appeal dismissed.
Sansregret’s belief in his ex-girlfriend’s consent was not reasonably held was to the risk that his ex-girlfriend’s consent might not be valid because she was afraid.
The mens rea for rape under s.1343(a) of the Code must involve knowledge that the woman is not consenting, or recklessness as to whether she is consenting or not, and, for s.143(b)(i), knowledge that the consent was given because of threats or fear of bodily harm, or recklessness as to its nature.
Wilful blindness and recklessness are distinct in that while recklessness involves knowledge of a risk and persistence in a course of conduct which creates a risk that the prohibited result will occur, wilful blindness arises where a person who has become aware of the need for some inquiry declines to make the inquiry because he doesn’t want to know the truth.
An accused can still hold an unreasonable belief and have the defence of mistake of fact available to him… however, he must not be wilfully blind in holding that belief.
R. v. Chase  2 S.C.R. 293
Man came into neighbour’s house, fondled her breasts etc… and tried to get her to sleep with him. When she fought back, he said that he was going to tell everybody that she raped him. He was convicted for sexual assault and the C.A. changed the conviction to common assault.