From what i understand, both from what i've read and past experience of halls at Reading (so not completely comparable), with a halls like Broadgate that have their own campus there are two different types of accommodation. There is the main set that is for the freshers, and they're all kept together, and then there are the smaller buildings on the same "campus" but not connected to that main hall, and that's where the postgrad students stay. I don't know if that's the case 100%, but i'd be very surprised if it weren't very similar.
I'm heading to Nottingham in September for a Masters in Public Policy and Broadgate is my top choice (that said i wanted some of the fun of halls as well as the serious side of the degree).