Not 100% sure but as far as I know wild camping on open access land in England and Wales is illegal
"On open access land wild camping is prohibited under Schedule 2 of the Countryside and Rights of Way Act 2000"
But in Scotland it is legal when done responsably (like over 100 ft fom roads)
"Part 1 of the Land Reform (Scotland) Act 2003 gives everyone statutory access rights to most land and inland water. People only have these rights if they exercise them responsibly by respecting people’s privacy, safety and livelihoods, and Scotland’s environment."
See the The Scottish Outdoor Access Code for more details of Scotland.