Trespassers on land

Questions:

• The trespassers who have been on my/council land have left behind a lot of rubbish, what can be done?
• There are some trespassers on a car park/ piece of council land, who do I call?
• There are some trespassers who have arrived on my land, what should I do?
• Why can't the police move the trespassers on?