Absolutely - self teaching on a PC based sim, without the re-inforcement of proper instruction beforehand, is going to introduce and solidify incorrect habits. The odds are that you will end up spending more on your flying lessons as a result, not less.
Yes, read up on the theory - it's sometimes dull, but very necessary as there will be exams to pass through the course. Getting hold of the CAA chart for the area (the one you want is called 1:500,000 South) and trying to understand that won't do you any harm either. It doesn't matter too much if the chart is out of date at the moment: although the current one is edition 42 and came out last month so should be good for the next year.
If you want to scratch the itch by doing things more specific to your lessons - read through the manual for the aircraft you'll be learning on. If it's Denham, it'll either be a Cessna C152 or a Piper PA28-161 I imagine - there are copies of the official manuals for both all over the web (if you're learning on the Cessna 172, ditto).
But really, really - stay away from PC based simulators. They may have value later - especially for navigation, but not early on when you still need to learn handling and basic airmanship skills.
G
N.B. I don't go there often at present, but did my instructor's course at Denham. Lovely spot and a well run school - you'll enjoy it. Don't forget to also learn about how good the cooking is next door in The Crewroom - I have a particular soft spot for their freshly made pizzas.
Last edited by Genghis the Engineer; 3rd Mar 2016 at 18:57.