HUNDREDS of rape cases could be reconsidered as and when the law on corroboration changes, according to the head of the prosecution service.

Frank Mulholland, the Lord Advocate, said rape and sexual offence cases which had not been prosecuted could be revisited in future if the Scottish Parliament abolishes the requirement of corroboration.

Mr Mulholland has previously said he would be strongly in favour of the abolition of corroboration because, combined with the Cadder ruling, there were fears the legal system was letting down victims of sexual offences.

The Cadder judgment by the Supreme Court in 2010 said it was a breach of the European Convention on Human Rights to let an accused be detained and interviewed by police without the right to a solicitor, but Mr Mulholland has said such shifts mean the human rights of rape victims may now be breached.

Mr Mulholland's comments come after a review of the criminal justice system by Lord Carloway, commissioned by the Scottish Government and published last year, recommended the centuries-old rule of corroboration be abolished.

Part of the reason for the recommendation was research from the Crown Office. It found more than 458 cases in 2010 where an accused person was placed on petition but where the case did not go any further because of a lack of corroboration.

Fiscals looked at a further 141 sexual offences not prosecuted in 2010, and found 67% had a good chance of a conviction had they made it to court. Mr Mulholland said it would not be appropriate to delay prosecutions in anticipation of the law on corroboration changing, but that rape cases not being pursued because of corroboration could be "revisited" in future.

"If the law does change and we have reason to re-look at them then we will," he told The Herald.

"I can tell you categorically we have not said we'll leave that until the law changes. That wouldn't be right. But what I can tell you is there have been cases where, as a result of Cadder, we have had to abandon live proceedings where we would have thought there would have been a reasonable prospect of conviction had we not had the Cadder effect.

"The real effect of Cadder is in making it much more difficult to prosecute rape cases."

Gillian Wade, head of the National Sexual Crimes Unit at the Crown Office, said they are mitigating the Cadder effect by making far greater use of different types of corroboration, and evidence from social media.

"People often conduct their private lives in an electronic format," she said. "The use of computers to conduct entire relationships is relatively new. That leaves a record. Where we think it is justified we can instruct the police to seize computers and mobile phones and chat logs and analyse that. We are increasingly inventive."

But she said there was "no doubt" that if corroboration was abolished it would remove a substantial legal hurdle in some cases.

She said: "I don't doubt that more would legally be able to proceed. If you have reported a rape and it's being investigated and there's sufficient evidence then that person will go on petition. If, because of corroboration, it can't proceed, then the option is still going to be there to look at.

"You are not closing the door and there is an option to go back depending on what the victim's views are later on and depending on the quality of the evidence.

"It's not the case that the victim is having to weigh up whether to wait or whether to proceed because if there is sufficient evidence then the Crown would be proceeding anyway.

"If there is insufficient evidence as a matter of law then there might well be options to revisit that case if the law changes, but it would be on a case-by-case basis.

"The fundamental message is that we are trying to get as many sex offenders convicted as possible. If there is an option for prosecution, either before or after reform of the law, then the Crown will take that option."

New figures show that between December 2010 and February 2012, 19 rape cases were indicted, resulting in 12 convictions for serious offences, 11 of them for rape or a serious sexual offence.

Eileen Maitland, of Rape Crisis Scotland, said: "The appeal which led to the Cadder ruling was underpinned by human rights legislation, and reflects a growing trend for discussions on human rights within the criminal justice system to focus exclusively on those accused of crimes.

"It is vital that we are equally vigilant with regard to the human rights of rape survivors, and that every effort is made to ensure that our legal system offers full and proper access to justice to those who experience this devastating crime."