OK I haven't done this paper, was going to be taking it next year but dropped it at the last minute so had already had a look at some of the reading, I would advise picking one book from each section and really reading it, maybe make brief notes on key themes/trends (stress brief - don't even do this if you think you will remember!) but you really wont need to do any more than that, after all everyone has at least a basic contextual knowledge of modern Britain just from common sense.
I love Taylor, so he would be my first choice from political/general, but I have Hope and Glory: Britain, 1900-1990 at home now and that seems to be fairly comprehensive, if a little lengthy.
For social, I would go for Change in British Society; haven't read any of them but it sounds like it will highlight 'turning points'/key themes i already mentionned, an you may even be able to skim it depending on the layout of the book.
Economic is my weakest aspect of history and I detest it so I personally would ignore this section entirely!! However I have 20th Century Britain: Economic, Social and Cultural Change at the moment and that again looks like a good place to start as you can pick and choose sections to look over without having to read the whole text.
International my choice would be Britannia Overruled, but I have no reason for this whasoever *shrugs*.
Basically, every specific essay will require very specific knowledge which you cannot be expected to pick up before your teachign starts (else what would be the point!) All this preliminary reading is simply to give you a reference point, so that when asked to write about, say, Thatcher's economic policy, you know who Thatcher was and the broad environment within which she was working. I would say preliminary reading is even less important for this period because you probably have that broad knowledge already, however being a little keen never hurt anyone! You don't need to own any of these if you can get them from local libraries, the SSL has multiple copies of all of them (and one extra once I return all of the ones I have in September!) and you will probably find most of those listed never actually come up on essay specific reading lists anyway, which will tend to be more focussed.
The edition of Tocqueville won't matter at all. Advice; before I arrived, I read the text, and wrote a summary (in english!) of each chapter, from the French edition, but checked wherever I was unsure of my language skills against an English copy in Oxford. A short summary, of no more than half a side A4, then filed the lot, so that when I got an essay I could flick through my short and sweet notes to the relevant chapters without having to go through the text again, only returning to the book to re-read and pick out quotes in the fortnight before my exam - I got a first on the paper and it was a lot less effort than reading the text as term went along!