It's generally not the law but rather the lawyers who are asses, but in the case of sexual offences, the law is too piecemeal to deliver consistent results, and is therefore an ass. No Home Secretary that I can recall has undertaken a thorough review of laws around sexual offences, and it shows.
For example, here new legislation has been introduced to facilitate evidence from vulnerable witnesses etc, some judges (because it's within their discretion) will veto screens and video evidence.
Some judges still allow forceful questioning about a victim's prior sexual history, even though it's long not been deemed a valid path evidentially, and serves mostly to prejudice jurors against victims.
Constant re-categorisation of various sex offences, in terms of the ambit of particular offences, and of sentencing guidelines, also have an effect, with judges having to rely on their clerks to keep them informed as to current practice.
It's all a big clusterfuck, and one that disproportionally affects women and children, but you won't find any Home Secretary willing to take on the issue because it's not a surefire vote winner.