For reference, the questions asked by the OP was:
”So, can I just get this straight - at the time Prince Andrew slept with the 17 year old Virginia Giuffre - was it illegal in the UK to have sex with a prostitute who was under 18? Was illegal to have sex with someone who had been trafficked? I know it is now.”
That’s a perfectly reasonable question. It’s not “what does an individual poster consider rape to be?”, it is “what does the UK law consider rape to be”. They are, obviously, not the same.
The answer depends on what the law was in the UK at the time the events at issue took place (March 10 2001). The law is not static, but changes from time to time, and new laws when introduced are not retrospective. So to answer the question entirely depends on the relevant law around sexual offences in the UK on 10 March 2001. Future changes to the law are irrelevant. We can fairly confidently say the same events, if they happened now, would likely be criminal offences, but that its a different question.
Sections 57-59 of the Sexual Offences Act 2003 introduced offences around trafficking into the UK for sexual exploitation. As these provisions were enacted after the events in question took place, they are not relevant here. This case would be looked at based on the law as it was before the Sexual Offences 2003 was enacted. Under this law, the impact of trafficking on consent was not considered.
The second important point is that to be guilty of a crime two separate elements must be proved: the criminal activity (I.e. that Andrew had sex with Virginia Giuffre) and the relevant mental state. For sexual offences, the CPS has to prove that the person being sexually assaulted/raped do not consent, and the accused knew this, or should have known this. This is a very technical area which has been reviewed time and again by the criminal courts - the upshot is that there is no simple test, each situation must be fully examined. I’ve linked to the CPS guidelines below on consent in case anyone is interested, so you can see how complicated an issue it is.
One point to note is that prior to 2003 there was a defence of a genuine though unreasonably mistaken belief as to the consent of the complainant - that has now been abolished. But that is relevant to assessing whether Andrew had the necessary mental state to make this criminal conduct in 2001.
So this isn’t an easy question to answer and requires a bit of legal archaeology. It’s an interesting question though, even though ultimately it makes no difference to people’s judgements on Andrew’s behaviour. He doesn’t need to have committed a rime for people to justifiably feel he has behaved appallingly, and that his consequences are deserved. Equally though, it’s not being an apologist to point out that his behaviour in 2001 may not have been criminal. That’s just a legal conclusion. You may not like it, but the law is what is it, not what posters want it to be….
www.cps.gov.uk/prosecution-guidance/rape-and-sexual-offences-chapter-6-consent