Whether you want to watch the stars without any light polution or want to reach the summit by sunrise wild camping might be for you.
Wild camping is legal in Scotland, England and Wales providing you leave no trace of your camp, camp away from any main paths, roads etc. and keep out of 'restricted areas' such as Loch Lomond.
It is however ILLEGAL to camp on dried out moors due to the fire hazard.
You should try to camp on gently sloping ground so that any water can run off the mountain, on firm (stone-free) ground and near a river. You should also pitch the tent with its tail into the wind. In the Lake District try to camp above 500m.
To wild camp you will need...