First things first - the Countryside and Rights of Way Act 2000 does not give anybody the right to wander where ever they want in open country.
What it means is that you can walk in certain mapped areas of mountain, moor, heath, downland and registered common land without having to stick to paths. But even that doesn’t mean that you have a right to walk a dog, or place a geocache, for instance
These areas are identified on the ground by this sign - and on Ordnance Survey maps by the following symbols
For the actual legislation, check here !