There are obvious problems with leaving stuff when halls are unoccupied.
I would advise that you move anything of value out even if the uni lets you leave it.
At Sheffield most catered contracts are for '31+7 weeks'. So you can't stay during the 7 weeks (Christmas, Easter) but you can leave your stuff in your room.
At Notts they make you totally empty your room every holiday. There are free storage rooms, which are locked when we leave, but they dont take responsibilty for anything broken/damaged etc. So prob dont want to leave too much in them.