I suppose they were here up untill very recently and without human persecution would've still been a naturalised species.I do feel however it would require constant monitoring more for wolfies sake than the local sheep.Anything that restores the natural balances of the UK countryside can't be a bad thing.It could be argued that creatures so high in the foodchain are a vital component of any balanced environment. But why stop there,following on from that the thought occurs would bears be sustainable?