that's spot on, you should always seek permission to camp.
you have right of access (under crow and various rights of way laws) to land and rights of way - to "Pass and re-pass" between different locations. If however you're staying, strictly speaking you're not adhering to the law.
The "blue book" is the ultimate guide to rights of way, and is the bible for rights of way departments. worth a read if you want to impress your asessor, though their knoeldge is seldom that good
i.e. it's legal to cycle on a bridleway, but not use a unicycle. it's legal to ride a horse, but not a llama... etc. access and rights of way are fantastically complicated!