E.g. opening hours and fences around parks - what the hell is that about? I was just totally confused the first time I got to a park in the evening and it was closed.
Part of it of course has to do with density, but to me that just makes it all the more important to protect and ensure as much access as possible. Instead people are herded into as little land as possible, and opening hours imposed on a good chunk of it.
Scotland does have similar rights to Scandinavia.
Hampstead Heath for example isn't.
Here's something to give you a taste of what is possible:
https://www.youtube.com/watch?v=opAWJnD0Jro&t=40s
https://www.visitscotland.com/accommodation/caravan-camping/...
Also if you don't fancy staying in a tent there is a network of bothies where you can stay for free (at least during normal times):
I see on TV people in Nordic countries camping by a lake and fishing for their dinner in complete solitude. I don't know where I could do that in the UK, except as some kind of paid bushcraft experience...or tresspassing!