It's a lot of hard work, hours of reading and analyzing and a lot of written work as well.
To progress to qualifying you would also need an additional year at law school which is very full on as well as being expensive and with no guarantee of a job at the end of it.
Competiton for legal jobs, especially training contracts (the two years on the job you need to qualify) is incredibly fierce.
As said above, you don't specialise at degree level (unless you want to go and do something like Criminology) but will do criminal as one of your core modules in the first year.
You will also have electives and should be able to do some criminal related ones such as evidence or criminal justice, dissertation etc... it depends on what the uni offers.
If you really want to go into criminal law then often a damn good dose of reality is what is needed. If being called out at all hours of the night to attend a police station to deal with all kinds of crap sounds like the kind of job you would be interested in then that's a good start.
I'd recommend going and sitting in the local Magistrates court watching something like bail applications, see the kind of work (and people) you would, in the main, be likely to be dealing with, at least at first, and watch the lawyers.