You cannot normally fly high in the UK, as Class A forces you down.
Only aorund places like London and Manchester and the occasional airway. Most of the time you can get to 55 quite readily, even quite close to London and if there is Class D then you can often get a clearance through. I agree though that Class A does put a dampener on things because there is no way to get a clearance through if it "doesn't touch the gorund".
If there is a layer of broken cloud, try and get on top because once up there *most* other people will be below it, and certainly all gliders. I came back across Wales a few weeks ago and went at 7500. There was a layer of Bkn at 4000-5000 so at 7.5k we were in the smooth in the sunshine, there was no one else around (saw a few others below the cloud) and no airspace worries. Plenty of holes to get back down through and Cardiff could see us from 100 miles away and quite happily gave us a traffic service.