Re: Key? No thank you.
"My place has a key which lets us all enter the main and rear entrance, cycle room etc but then lets us in to our individual flats."
That suggests that the individual flat keys only differ from each other slightly.
Some fellow-students once tried to make a master-key for the fire-doors to their flat in halls, by carefully comparing keys and mechanisms. They discovered they'd made a key that opened all the doors in that tower block. And university campus. And BBC White City, various major rail stations.... Fortunately they were very responsible and only issued master keys to people they liked.