Bob has only admitted to the crime of voyeurism if he says he filmed the encounter for his (or someone else's) sexual gratification. This is a necessary element of the voyeurism offences in SOA 2003. Instead he will say of course not, he would never do such a thing, the recording was solely for the purpose of protecting himself against false accusations, like this one.

@Lag It's a good point, but I think for the purpose of this question we should take the rape / voyeurism as just examples to illustrate the question of whether or not a person can be punished for committing a crime if the act of that crime provides a defence to another crime. Our assumption therefore should be that both of the crimes did in fact take place and can be proved.

Don’t forget that rape is still possible if the people involved are intoxicated and can’t give proper consent, or at least that is my understanding in many places around the world.

@JoeW The premise of the question is that "the film makes it clear sex was consensual" so we don't need to be concerned with issues that might make it non-consensual.

@JBentley and that premise is deeply flawed as there are things that can invalidate what might seem as consensual in the video. A full investigation would still be required and the video itself can’t be used to clear the person in question.

@JoeW And that could well be the basis of a good, but different, question. The question here is whether or not you can be excused from a crime if that crime gives you a defence to another crime. It's pointless to pick apart the premise, because then we're looking at an entirely different question. The assumption, for the purpose of the question, is that a full investigation has been carried out and the video has convinced the police or the CPS that there was no rape. Given that assumption, will Bob get in trouble for making the video?

@JBentley regardless it shouldn’t just be hand waved that the video will clear the person of charges. A full investigation would still be required for both points 1 and 2 before anything can be decided and a simple outcome cannot be declared based upon the information that we have from the question.

@JoeW Yes, it can be hand waved. Otherwise every legal question would get bogged down in the entire background leading up to the premise. For example, a question like "In contract law, if I accept a validly made offer, is there agreement?" should produce the answer "yes". It should not produce a side-debate on whether or not the offer was in fact validly made because the whole point of the question is that we're assuming it was. That's in spite of the fact that in real life we would have to look at the offer to make sure it meets the necessary elements.

@JBentley it should be included in the question rather than making an assumption that the video will actually get the charges dropped. It does make a very critical difference in the answer b

I don't understand why you specifically mention Rape is a crime when there was clearly no rape here.

The two wrongs described in the question are the filming without consent, and the false accusation. But neither party can plausibly say that their criminal act was justified by the other's criminal act, because each party committed their crime without knowledge of the other crime. Bob recorded the film before Sue made her false accusation, and Sue made her false accusation before she knew about the film. In the usual sense of the phrase "two wrongs don't make a right", the second wrong is done with the intention to correct the first wrong, but that isn't the case here.

Why is it a crime to have a surveillence camera in one's own home? If it has to be turned off until those entering have given their consent, it sort of defeats its purpose.

@WeatherVane See Guidance on the use of domestic CCTV. One requirement is "putting up a notice informing people that recording is taking place". In the scenario described by this question, that isn't done; Bob records Sue without her knowledge.

@kaya3 That article starts with "If your CCTV system captures images of people outside the boundary of your private domestic property" (typical example: doorbell cameras). It doesn't seem to cover recordings inside the private domestic property.

@kaya3 suppose I suspect that my landlord lets himself in to my home when I am out. I install a surveillence camera, but if I put up a notice, he won't come in. That may stop it, but I'll never find out the truth. And if things have sometimes "gone missing" there is nothing I can do about catching him.

@WeatherVane It is not "a crime to have a surveillence camera in one's own home". It is a crime to secretly film someone "doing a private act" for the purpose of one's own or a third party's sexual gratification without the someone's consent to that purpose.

@Lag but surely if the camera is in my bedroom, and I know it has a view of the bed, and then proceed to have sex with someone, that cannot be legal. Even if I somehow convince the judge that I only have a camera in my bedroom to protect myself from being accused of rape (which would take some convincing), I still recorded someone without their consent, and surely that's illegal in many (most?) jurisdictions, is it not?

@terdon I don't think it's an offence in England and Wales, but of course I could be wrong.

@Lag I am very much not a lawyer, but it looks like taking videos of people without their consent is illegal in the UK if they have a reasonable expectation of privacy (1,2). I struggle to imagine a situation where one might have more of an expectation of privacy than when having sex in your lover's bedroom, so I feel it would indeed likely be illegal.

@terdon Breaching "expectation of privacy" tends to be a civil matter.. AFAICT neither of those articles specify nor link to a relevant criminal offence. The first article seems very low quality in that it links to articles on the same website that are irrelevant to the hyperlinked text.

I’m voting to close this question because each question should be in its own individual post. This post poses too many questions to be properly addressed. It should limit its scope and get split into several individual questions.