Best go into an Apple store and compare the iPad Mini to the normal iPad and see which size you prefer. Then decide if you will be using it mostly at home on wifi (or other places where you get free wifi) or whether you really need it to work anywhere (i.e. pay more and get the 3g version).
iPad mini starts from £269 and normal size iPad from £399.
Wait till after Tuesday, when new Apple stuff is being announced. There are rumours of a new thinner iPad and older ones may be reduced. Of course, lots of Apple rumours turn out to be rubbish, but I think it's worth waiting two days.
Apparently Apple have been advertising jobs in a prospective Edinburgh store since April, but no confirmation yet of when or where. Iirc they were advertising for jobs at the Reading store up to a year before it opened. They do have stores in Glasgow & Aberdeen, which are a little closer than Covent Garden! Or there's a Stormfront store in Stirling -they are Apple suppliers and usually have them to try (at least the one near us does)