Hi John,
Wild camping is strictly illegal in England & Wales. That's what the law says, but in practice, many people do wild camp and ensure that they do so by following the practice of camp late, strike early and leave no trace. In Snowdonia, the Peak District and the Lake District, there is a tolerance (but not a legal right) for wild campers to camp above the intake wall. One must never ever camp in the same location for more than one night and by following the unwritten rules of ethical wild camping, most will have a good experience and no issues. If one were to be found, then the landowner can ask a person to leave and that is what a wild camper should expect to do.
On my Heart of Wales Line Trail backpack I sought permission to camp wild at one location by speaking to a farmer who was very supportive and understood the ethics of good practice wild camping. On other occasions I tucked myself out of the way, arrived late and left early. On another occasion I camped above the intake wall on the side of a hill. In all the times I have wild camped in the UK, I have never had an issue with any landowner due to the unwritten rules that I have followed. Interestingly, whilst on my latest backpack, I had a long conversation with another landowner who supported the idea of a person on a journey stopping for the night before moving on the next day. The issue of wild camping has been brought starkly into focus this year due to the unethical behaviour by a number of people who have caused damage to the land and left their detritus when they have left an area. This has been commented on by several newspapers who have recognised that some people really are behaving rather badly in the countryside.
The law in Scotland is different and wild camping is legal albeit with certain criteria to be followed. I have added a link to the rules here.
https://coolcamping.com/news/259-is-wild-camping-legal-in-scotland
Hope this all helps.
Regards,
David