I think that the A Level is useful for two reasons:
1.
It's been said many times that the worst thing you can do is to go to university to study law without knowing it's for you - doing an A Level over two years gives you an indication as to whether or not it's something you're interested in
2.
It gives you a basic level of knowledge that, in my experience, is helpful to give you a bit of a head start when you're trying to find your feet in a new environment
The official policy is that the A Level "offers no particular advantage or disadvantage"
to your application; I interpret this as meaning that the university won't favour people with it. That's not the same as the subject not giving you an advantage when it comes to reading law at university.
As part of the AS, I looked at the role of lay people and legal professionals within the legal system and learned about the court structure and appeal routes, which is useful when you're reading a case to know whether or not there's a chance that the decision was reversed by a higher court (the name "Court of Appeal" suggests to a layman that it's the highest court in the land, which isn't the case!). I also did a little bit of tort law (negligence) and some criminal (non-fatal offences); admittedly this wasn't a lot and was pretty superficial but it did help to whet my appetite for the A2.
For the A2, centres offer different subjects, with there being options in Tort, Human Rights, Contract and Criminal to name but a few. I did Criminal and therefore looked at homicide, non-fatal offences (in more depth), property offences, defences and a little bit of jurisprudence. The jurisprudence hasn't really been that useful yet, but contrary to the myth that "it only gives you a two-week advantage", I think the A Level - if taught well - gives you a good grounding. Of the eight supervisions I've had this year, I'd already covered the work for about five of them at A2 (although naturally more reading was needed to refresh my memory and deepen my understanding). I've only come across one fundamental area of contention with my supervisor from my existing A Level knowledge over the course of my study, which even then is an area over which academics are divided, whereas my peers still had to get to grips with the basic concepts. Becoming familiar with the language is good too - it just makes you feel more at ease.
I think that part of the problem is that with Law being a relatively new A Level, universities are still wary of it to an extent since the teaching is so variable. I actually started the AS as part of an evening class in Year 11 and the teaching was appalling - I got an E in my first exam (predicted an A) and an A and C in my others (the A was a sheer miracle because that was an essay paper; the C was on the substantive law that we hadn't really been taught). I then convinced my sixth form to allow me to self-teach a resit and take up the A2 in my first year, and they couldn't have been more helpful. Of the five papers I resat there, I got 100% on all of them thanks to their help. It just goes to show that there must be some value in the A Level, and I'd hope that my UMS marks would act as a testament to my understanding!