Books to read for econ applicant who hasn't done econ?

Hey guys,
I am going to apply for LSE for undergrad economics and/or finance(most proably economics). Unfortunately none of my previous schools have offered economics as a subject. I currently am studying in Scotland for 3 Advanced Highers in Maths, Physics and Computing.

I know that it is good to read a book on your course and comment about it on your PS, so I am just wondering if anyone knows any good books regarding economics/finance that I will be able to understand and which is helpful to my understand of economics.
I have researched basic economic principles(supply & demand, diminishing returns), I just want to further my understanding so I have something to talk about in my PS.

In regards to my PS, is it OK if I talk about what I want to learn in the course instead of what I already know? Because I have seen some economics personal statements from LSE and some of them go quite in depth in the subject, e.g. commenting about the financial crisis of '08, however I cannot go that far as I have not explicitly studied it.

Finally, what things can I do in the few months until submission day outside or inside school that will look good on my application?
Unfortunately my city is not known for banking so it is exceptionally hard for me to find any banks taking in school students.

Thanks!