In reply to MountainGal:
Go high and off the beaten track. Best if your tent is not visible from any roads. If you are staying in one spot for just one night at a time you shouldn't have any trouble. If you want to install yourself somewhere for like a week then go find a campsite.
Used to camp behind the boulders a while back - the grumpy bloke who comes round claiming to be the owner and demanding money only ever turned up at weekends in the summer though.
Probably more scope in the Carnedds than anywhere else. Make sure it stays that way by leaving no permanent trace please.
Don't forget the hot water bottle!