It is allowed, with conditions, in Scotland.

http://walking.visitscotland.com/usefulinfo/wild-camping

One restriction that I know of is that [camping is not allowed on the eastern shore of Loch Lomond][1]. There are likely to be restrictions during the hunting season as well, there are phone lines where you can find out about hunting activities.


  [1]: http://www.bbc.co.uk/news/uk-scotland-tayside-central-12698722