IT is said that rape is the easiest charge to make and the most difficult to prove.

The first part of that common assertion is uncertain but the second is indisputable, especially in Scotland as the law is currently constituted.

Last year the number of rapes and attempted rapes reported to the police reached a five-year high but the number of convictions tumbled to a 10-year low, down 31% on the previous year. From 54 convictions in 2009 to 2010, it fell to just 36. These are terrible figures after successive Scottish administrations have invested an enormous amount of effort in improving the country's scandalously low conviction rate for this terrible crime.

The Sexual Offences Act, brought into force last year, was intended to clarify the law and improve the chances of rapists being prosecuted successfully. This was supported by the establishment of a specialised unit in the Crown Office.

Then came the Cadder ruling, the UK Supreme Court judgment that stopped police questioning suspects who had not been offered access to a lawyer. At the time there were warnings that the ruling would make it more difficult to put rapists in the dock. This is because prosecutions in Scotland often relied for corroboration on admission by the suspect that he had had sex with the complainant, even if he maintained that she had consented. Now rape cases cannot proceed on the basis of such admissions. In fact, the statistics suggest that last year's conviction rate would have been even lower had it not been for the new National Sexual Crimes Unit. (Of cases coming to court, the conviction rate has improved since the unit began its work and the overall conviction rate for sexual offences is 69%. This is encouraging.)

However, these figures will concentrate attention on the issue of corroboration, a unique feature of the Scottish legal system, and the recommendation by Lord Carloway in his recent report that the strict requirement for it should be abolished. Rather, cases should be decided on the quality of the evidence. This is a vitally important issue in cases that rely largely on the word of one person against another.

Defenders of corroboration maintain that abolishing it would end the presumption of innocence until proven guilty, as several legal experts told MSPs examining the recommendation yesterday. However, Professor Fiona Raitt of Dundee University told the Holyrood Justice Committee that abolishing corroboration would address "a long-standing deficiency in Scots law, namely the lack of a satisfactory response to women and children who bear the brunt of sexual offences". One thing is certain. In the wake of the Cadder ruling, the status quo on this issue is untenable.