On common land I have had good results with the "Turn up, make camp in a quiet place as the lights fading and break camp shortly after dawn" method.
What are they going to do to you anyway, ask you to move on?
Shucks, that's a hardship
When doing this by motorcycle/car it can be combined with the "cracking open a beer then saying sorry but I can't ride in this condition" method.
Jeez we own the bloody countryside in a roundabout way, stop being so British about it.
This only applies to common land though blah blah blah usual disclaimers.