In reply to Groundhog:
I'm not familiar with Kinder Low, but I assume this is open moorland? If so farmers with sheep grazing rights on that moor will be able to graze sheep on there.
It is not unusual to put hardy sheep out on the hills in winter where they can be fed hay later when there is snow on't ground or brought off the hill if the snow is likely to stay.
Why do you think they should not be there? If you think this grazing is 'illegal' in that the owner of the sheep is causing them to trespass on land not belonging to the owner of the sheep, it is a civil offence and the police cannot really get involved. In which case you will have to find the land owner, probably an estate, or simply go to a local farmer and ask him/her who manages or controls the grazing.
It may also be the case that the land is controlled by a court leet - but your farmer will know for sure.
Post edited at 17:50