There are two items from Canada that are worth the read.
Marie Deschamps, C.C. Ad.E., External Review Authority, External Review into Sexual Misconduct and Sexual Harassment in the Canadian Armed Forces, March 27, 2015.
Under the standard articulated by Criminal Code and the Supreme Court of Canada, genuine consent may be communicated by word or conduct. However, where either party indicates by any means—verbal or not—that he or she is uncomfortable or reluctant to continue with the sexual activity, an obligation crystallizes on the other party to specifically obtain consent before proceeding any further. While the Court did not explicitly require that this consent be verbal, as a practical matter where there is doubt as to whether or not a party has consented to sexual activity, the only clear way to dispel such doubt will be to verbally seek consent.