"Right to roam" in England and Wales is limited to those areas dedicated as "Access Land" under the CRoW Act 2000. This land is shown on the O/S 1/25000 Explorer maps by a yellow-orange wash with an orange border. It isn't shown on the 1/50000 Landranger maps. There is certainly no "general" right to roam, so I'm not surprised some farmers are getting hacked off if that's what some walkers think.
Access Land can be temporarily closed (although it has to be signed to make this clear), e.g. for forestry works or particular breeding seasons, etc.
Existing "definitive" public rights of way - footpaths, bridleways and byways - are not part of the CRoW provisions, but continue unaffected. It is illegal to obstruct a right of way.
Needless to say, Scotland is far more enlightened.