Tri posting for the win, haha.
OK so here's an update. Went into Comet today to have a general look round. For those of who don't know, Comet is an electrical store, we have loads of them round here. They had various cameras up for display, including both the 1100D and the 550D (and Fuji's new SL cameras which I had never seen before). Had a play with both the 1100D and the 550D, sadly I couldn't turn them on though because they didn't have batteries, but I could get a feel for them.
They were pretty similar in looks and size (the biggest difference was the 1100D was in some sort of cherry red colour scheme) but the cameras felt a bit different, notably the 1100D had a more "plasticy" body. Didn't bother me though, I thought the size and weight was quite nice. Comet are selling it with the IS lens for about £360 and the 550D with the IS lens is £500 IIRC.
Alternatively, one of my friends has a D5100 which she never uses, so I may see if I can make an offer...
EDIT: Asked for a quote on her D5100 if she doesn't mind selling it. We'll see what she comes back with.
EDIT 2: She can't sell me the D5100.