That a woman may "freeze" rather than fight back against a sexual assault is a common and well-documented reaction.

She might judge her attacker as too dangerous to take on; she might be temporarily paralysed and unable to move or scream; she might even reasonably believe the only way out is through — to endure the rape and "get it over with" rather than risk escalating or prolonging it.

This response — and the fact that not fighting back does not mean someone is consenting — is also recognised in Australian rape laws, which have been reformed and refined over the years to better reflect social attitudes towards consent.

Consent cannot be established, in other words, by pointing to a complainant's lack of physical resistance: "She didn't forcefully say 'no', so that means she said 'yes'."

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But in Queensland, a century-old legal loophole is allowing defendants in sexual assault cases to escape accountability by doing exactly that.

And, according to some legal practitioners, it is not only undermining the state's robust and progressive definition of consent, it is also deterring potentially thousands of victims from reporting sexual assaults and police from pursuing charges: why bother going through such an arduous process if you know you're unlikely to get justice?

In practice, the "mistake of fact" defence is being used by sexual assault defendants to argue that, even if the complainant did not consent to his sexual advances, he honestly and reasonably but mistakenly believed that she did — and secure an acquittal.

In a number of recent cases, defendants have, for instance, cited their own intoxication to support their use of the defence, effectively arguing they were so drunk they thought the complainant was consenting.

In other cases, the complainant's intoxication has been cited — even when she was so inebriated she was legally incapable of giving consent — with the defendant claiming she was so drunk he thought she was freely participating.

'Worst state for sexual assault complainants to get justice'

For at least a year, survivors and advocates have been calling on the government to conduct a review of the state's sexual consent laws, particularly the mistake of fact defence, which they say is failing vulnerable complainants including children, women with disabilities and domestic violence victims.

But their appeals have so far failed to elicit more than brief acknowledgment from the Attorney-General Yvette D'Ath, who has said the government had "undertaken a process of consulting with legal stakeholders" whose views were "under consideration".

Now, frustrated by what she says is an "unacceptable delay", law graduate and author of Eggshell Skull Bri Lee is launching a new campaign which she hopes will inform more people about how Queensland's mistake of fact defence is being used by both "calculating, predatory offenders, as well as the reckless and opportunistic ones" to evade responsibility, and pressure the government to finally take urgent action.

'I have a really deep sense of injustice that it is just so much harder for survivors in Queensland than in other states,' says Bri Lee. ( Darcy Starr )

"Queensland is the worst state for sexual assault complainants to get justice," Ms Lee, 27, told ABC News.

"Our mistake of fact laws are the most archaic of any state or territory in Australia ... and so all of these decades of hard work to improve the definition of consent are being completely undermined by this defence."

It's "absurd", she said, that it is easier to defend rape allegations in Queensland than in other states, and "very frustrating" that for every passing month the matter is not addressed, "dozens more women who survive sexual assault are being affected".

Together with Bond University Law Professor Jonathan Crowe, Ms Lee has created a website that explains why it is "extremely difficult" to secure a conviction in rape cases involving the "freeze" response, intoxication, mental incapacity or language barriers — factors commonly used by defendants relying on the mistake of fact defence.

'Reform is so urgently needed'

The site's content is based on a comprehensive study by Ms Lee and Professor Crowe of the role of mistake of fact in Queensland rape and sexual assault law, in which they conclude the defence should be "rendered inapplicable" to the issue of consent in rape cases.

At the very least, they argue, reforms should be introduced to limit the use of the defence in line with laws in Tasmania, which preclude defendants from using mistake of fact if they were "reckless as to whether or not the complainant consented".

"Reform is so urgently needed," said Ms Lee, who is urging the Attorney-General to refer the matter to the Law Reform Commission. "It is really frustrating how long it is taking the government to do something about this issue."

Reforms could be easily introduced, she added, "because we have the blueprints of other states that have already done it. We're not reinventing the wheel; what we're fighting for is not unprecedented."

Among numerous egregious cases detailed on Ms Lee and Professor Crowe's website is Phillips v R.

In that case, the complainant, a 13-year-old girl, was asleep in her bed when the defendant, a 21-year-old friend of her step-brother who was staying the night, came into her room, climbed on top of her and allegedly raped her as she tried to push him off.

Similar incidents happened on three other occasions — two of which she did not resist, though she was still not consenting — at which point the girl told a counsellor and the defendant was charged with rape and unlawful carnal knowledge as alternatives, as she was below the legal age of consent.

However, in defence he argued the girl had consented to having sex and that, even if she hadn't, he mistakenly believed she had.

In the end, the Supreme Court found it was open to the jury to apply the mistake of fact defence, and the defendant was acquitted on all four counts of rape, though he was found guilty of unlawful intercourse with a minor.

"I challenge anyone to read that case, her testimony, and think for a moment that the defendant ... didn't know what he was doing was not okay," said Ms Lee, adding that many of the cases she and Professor Crowe had reviewed involved women who testified that they had been asleep before waking up to the defendant raping them.

"It is completely understandable and entirely reasonable that they have that [involuntary] freeze response or decide not to fight back because they don't want to put themselves at risk of [further] violence."

Do people 'care enough' to take action?

The Attorney-General Yvette D'Ath did not respond to specific questions from ABC News about to what end the Government was "considering" the views of legal stakeholders in Queensland, or when the outcomes of that process would be made public.

Sexual assaults were "particularly heinous crimes", she said, and people who commit such offences must be held to account. "Victims carry the emotional scars of what has happened to them for life and they deserve better than rash decision-making," Ms D'Ath said.

"The Palaszczuk Government is considering the views of Queensland's foremost legal stakeholders and reviewing dozens of Court of Appeal judgments handed down since the definition of consent was previously amended almost 20 years ago," she said, adding that the government had "a proud record of reform in the area of sexual violence and supporting victims".

But Ms Lee, who regularly copies the Attorney-General into her advocacy tweets, said she intended for her campaign to continue "shaming the government" for stalling, and hoped a letter-writing "gathering" being held at Brisbane Square Library at the weekend would encourage members of the public to join in.

"If we can get enough people writing letters and emails [to the Attorney-General] about this issue, it will demonstrate that people care enough to do something about it," she said. "Politicians will listen to numbers."

Ms Lee, a survivor of sexual assault herself, also has a personal connection to the subject, which she has detailed in her multi-award winning memoir, Eggshell Skull.

She was first alerted to the impacts of the mistake of fact defence while working as a judge's associate in the Queensland District Court in 2015. This, she said, meant running a new trial and overseeing a handful of new sentences every week, the vast majority of which were for sexual offences.

"I saw so many acquittals that I thought should have been convictions ... particularly when intoxication was a factor, and I started researching mistake of fact and found that actually Queensland was the worst state [for complainants]," she said.

'I AM ANGRY, I AM ANGRY, I AM ANGRY'

The first time she saw a defence barrister explain the differences between consent and mistake of fact, she said, is seared in her memory.

In that case, the complainant, an "imperfect victim" of nervous disposition who stuttered her way through her evidence in chief, had woken up to find a man inside her, but didn't scream straight away because she assumed it was her ex-boyfriend — until she came to and realised the shape in the dark above her was actually a friend of his.

Struck with fear, she cried out, pushed him off and ran into the bathroom, locking the door behind her.

In court, however, the defendant argued that the woman was extremely drunk, Ms Lee writes in her book, and "not only consented but also initiated the sex, and that either (a) she was awake the whole time then changed her mind and 'went nuts', or (b) she passed out and he kept going, mistakenly believing she was still conscious".

"I don't like mistake of fact," Ms Lee writes, "because it gives juries an easy reason to acquit. They can say, 'Sorry love, you didn't ask for this', but simultaneously, 'He's not responsible for his actions'."

Perhaps unsurprisingly, the notebook Ms Lee was using during that particular trial finished with nine words: "I AM ANGRY. I AM ANGRY. I AM ANGRY."

"I have a really deep sense of injustice that it is just so much harder for survivors in Queensland than in other states," Ms Lee told ABC News, four years on. "It's so unfair."

If this story brings up issues for you, there are people you can talk to. 1800 RESPECT deals with sexual assault. If you don't want to talk, you can access their website. You can also talk to Lifeline Australia on 13 11 14 or access their website.