I wouldn't go in blinkered right now, it's not a very profitable area of law. Plus you might find you like commercial law as well/instead if you study it at Uni.
You could just look at revision aids for A Level Crime Special Study in the Law syllabus? No point in looking at a textbook for Undergraduate level, they're tricky and it gets quite dry and dull.
The one you'll most likely use at Uni is Smith & Hogan Criminal Law. It's the size of a dictionary and 90% of it isn't relevant.
Watch 24 Hours in Police Custody, especially episode one which you can find by stealth and subterfuge on the illegal internetz.
If you want some drama and irritatingly inaccurate court etiquette but a little bit of Law, watch "Silk". It's about the Criminal Bar, but still a good watch.