Of course, rape is a terrible crime and gang-rape is one of the worst things that human beings can do to another person.

So, had four young men who were arrested after a group sex session at a student ball been found guilty of sex crimes, they would have been jailed for many years.

But the case against the quartet collapsed this week after detectives were accused of 'cherry-picking' evidence to support the prosecution, while 'airbrushing' anything that suggested the men were innocent.

Lawyers for the four students (who had been charged after the drunken sex session during a May Ball at the Royal Agricultural University in Gloucestershire) argued that evidence had been 'withheld' by officers before the trial. This included messages taken from the victim's phone hinting that she may have consented.

BARBARA HEWSON believes our criminal justice system, once insensitive to rape victims, has swung too far the other way and assumes an accusation by a woman is as good as proof of guilt.

It also emerged that the alleged victim had given 'different accounts' as a witness in another rape case involving an Army officer — also acquitted.

How could the police and the Crown Prosecution Service (CPS) have got it so wrong?

I have worked for many years as a human rights and civil liberties barrister and I'm afraid that I do not think this case can be dismissed as a one-off.

Sadly, it illustrates a deeper problem in our justice system when it comes to sex crimes.

Having once been deplorably insensitive to the problems that rape victims face, I believe that our criminal justice system has swung too far the other way. It now assumes that an accusation by a woman is tantamount to proof of guilt.

Even worse, it has encouraged sharp tactics on the part of the police and the CPS who are keen to have a more positive image as being tough on sex offenders and winning more successful prosecutions.

The most grotesque example recently involved Scotland Yard's VIP paedophile murder inquiry — and investigation into claims that a string of Establishment figures were responsible for killing three boys in the Seventies and Eighties. Though the probe collapsed, the police refused to say sorry to those whose lives had been ruined or reputations shattered by a suspected fantasist called 'Nick', whose claims triggered the investigation. Most controversially, one of the investigating officers, Det Supt Kenny McDonald, had described Nick's delusional ramblings as 'credible and true'.

The fact is that our criminal justice system is supposed to be founded on two critical principles. First, the presumption of innocence. Second, due process: the belief that criminal accusations must be proven beyond reasonable doubt, by fair procedures.

The system has encouraged sharp tactics on the part of the police and the CPS who are keen to have a more positive image as being tough on sex offenders and winning more successful prosecutions, she writes

However, when it comes to sexual assault, decades of campaigning by feminists and more strident members of the victim lobby have browbeaten judges and policy-makers into a change of approach.

The prevailing attitude seems to be that it is unfair to anyone claiming to have been the victim of a sexual attack that they should have to accept that their alleged attacker is 'innocent until proved guilty' and that the case has to operate under due process.

As a result, the system has been re-engineered to make it more difficult for the accused to defend himself.

Even the definition of rape has been changed. Previously, it was a defence for a man to show that he honestly believed the woman was consenting.

But the Sexual Offences Act 2003 — passed by the Labour government — introduced a so-called test of reasonable belief in consent. This means that the accused has to show he took reasonable steps to ensure that the woman consented to sex.

This has led to the ridiculous situation whereby some students demand 'affirmative consent'. This means that consent has to be sought and given at every stage of any sexual encounter.

Most ridiculously, students at one U.S. high school have been told that men should obtain consent every ten minutes during sexual activity. A further worrying development is that the police and CPS seem to see themselves as advocates for complainants — though they should be acting impartially.

The result is that they appear to shut their eyes to any evidence that might complicate their plans to bring a prosecution. This phenomenon is known as 'confirmation bias'. This was confirmed by the absurd admission of one Manchester barrister who said: 'If someone complains, we prosecute.'

The fact is that our criminal justice system is supposed to be founded on two critical principles - the presumption of innocence and due process, writes HEWSON

I'm sorry, but such a perverse attitude is highly dangerous. No one benefits when innocent people are wrongly accused.

The fact is that this creates a new class of victim: the falsely accused, or those who are prosecuted, who are presumed guilty until they can prove their innocence.

Some high-profile examples of those wrongly accused of sex offences are Nigel Evans MP, radio presenter Paul Gambaccini, war hero Lord Bramall and former MP Harvey Proctor.

Significantly, the legal authorities' attitude was outlined by former Director of Public Prosecutions Sir Keir Starmer.

In an article for the Criminal Law Review in 2014 written after he had left the post, he explained how changes were needed to improve the way the credibility of alleged victims was assessed.

He called for 'a more sophisticated approach that starts with the assumption that the victim is telling the truth'.

Sir Keir has since been elected as a Labour MP. But the pressure to believe all complainants began before he was appointed DPP.

Back in 2002, the Metropolitan Police issued a Special Notice 11/02 entitled 'A policy for the investigation of rape and serious sexual assaults'.

It began: 'Principle 1. It is the policy of the Met to accept allegations made by any victim in the first instance as being truthful. An allegation will only be considered as falling short of a substantial allegation after a full and thorough investigation.'

This approach encapsulates the problem. When the word 'victim' is used before a crime has been proved in court, it means there is a presumption of guilt. Equally, what happened to the promise of a 'full and thorough investigation'?

Some high-profile examples of those wrongly accused of sex offences are Nigel Evans MP, radio presenter Paul Gambaccini, war hero Lord Bramall and former MP Harvey Proctor

I am aware of many sex attack cases in which defendants and their lawyers have complained that when they provided the police with evidence suggesting that a complaint of sexual assault was false, the police simply ignored it.

For example, there was a case in which a teenager was accused by a girl of a similar age of raping her. As part of his defence, the accused boy's mother went through social media postings that her son and the girl had made during the time in question.

They showed that every time the girl claimed she was being attacked, she and the boy were in different locations. Yet despite this research being given to the police, the officers later returned it as 'unused material'.

Though the case went to trial, the accused's mother handed her dossier to the CPS barrister, who said they had never seen it before. Separately, it became clear that the girl's story didn't add up.

Within 24 hours, the prosecution barrister told the judge that the complainant was no longer regarded as a witness of truth and the trial collapsed.

However, things should never have been allowed to reach that stage. The boy's family incurred very substantial legal costs, which they were unable to recover from the CPS.

I believe that such people who are falsely accused and who are put through unnecessary and traumatic experiences should be able to sue the police for damages — compensation for negligent investigations. This is allowed in Canada.

Should those who have been falsely accused have even more right to redress? For example, ought they be able to sue the CPS if they feel their case has been mishandled?

Theoretically, it's already possible to sue public officials for misfeasance, but that requires proof of bad faith — something that is a very high threshold to cross.

Regardless of the redress that might be available to those who are wrongly accused, there is a much more important principle at stake.