Canada's so-called rape-shield law, which aims to protect sexual-assault complainants from unfair and irrelevant scrutiny of their sex lives, cannot be used to prevent an accused from mounting a reasonable defence, Ontario's top court ruled on Wednesday.

As a result, the court quashed the sexual-assault conviction of a man whose lawyer was barred from cross-examining a woman on her pregnancy and ordered a new trial.

In its ruling, the court acknowledged the critical importance of protecting complainants from questioning about their sexual activity when that activity does not form the subject matter of the charge.

Among other things, the court said, the rule takes into account the privacy interests of a complainant and was prompted by concerns about deterring victims from going to police and about feeding rape myths.

Times when 'questioning must be permitted'

"Notwithstanding these powerful considerations, there are times when such questioning must be permitted," the Appeal Court said. "This is one of those cases where a proper balancing ... requires that such questioning be permitted."

The Crown's position amounted to this: 'We say you are the only one who could have impregnated the complainant but you are not allowed to question her about whether this is true.' - Appeal Court

According to court documents, the accused, then 20 years old who can only be identified as R.V., was on a family camping trip in July 2013 when his cousin, 15, said he lured her to a washroom and sexually assaulted her in a shower stall. She then said she blacked out. R.V. denied any sexual contact with her.

A key part of the prosecution's case was that the teen's subsequent pregnancy corroborated her allegations — that only the accused could be the father. The young woman subsequently terminated her pregnancy and the fetal remains were destroyed, making it impossible to confirm paternity through DNA testing, court records show.

The defence applied in a pre-trial motion to cross-examine her on her other sexual activity as a way to attempt to refute the proposition that R.V. had impregnated her during the sexual assault. However, the judge hearing the application refused to allow the cross-examination.

'Patently unfair outcome'

In October 2016, Judge Robert Gee convicted R.V. after upholding the earlier ruling as binding on him.

Both those decisions were in error, the Appeal Court said.

While the prosecution did not dispute the relevance of questioning the teen about whether others might have made her

pregnant, it argued the proposed defence questioning would have been excessive.

"The Crown's position amounted to this: 'We say you are the only one who could have impregnated the complainant but you are not allowed to question her about whether this is true'," the Appeal Court said. "This is a patently unfair outcome that cannot be justified in the circumstances of this case."

The higher court said the pre-trial judge was wrong in finding that R.V.'s attempt to question the teen amounted to a "fishing expedition" despite knowing exactly what the cross-examination would have entailed.

'A substantial wrong'

"The urgency of vetting the Crown's paternity allegation during trial was simply too great, and there was nothing in the

circumstances of this case to diminish it," the Appeal Court said.

"The prejudice to the administration of justice of permitting the cross-examination, although real, was not intense enough to overcome that need."

The Appeal Court also rejected the prosecution's argument that R.V.'s lawyer had nevertheless managed a solid defence by skirting the cross-examination ruling and asking the complainant about her virginity.

While the questions were improper and should not have been allowed, the ruling still prevented the defence from asking further relevant questions, the court said.

"What occurred was not a fair substitute for the cross-examination that should have been allowed," the Appeal Court

said. "A substantial wrong or miscarriage of justice occurred."