I take it you are talking about the old boxes. All the equipment was given to the customer so technically it does not belong to sky.As to sky, we took the gear with us when we moved, but sky was not interested with the old equipment they supplied all new, technically it belongs to them, but they simply did not want it.
Things changed with sky Q. Q boxes are never gifted to the customer (though the dishes still are) and have to be returned at contract end.