Also, if you go behind the West Block in the Parliamentary Triangle* you will find a most satisfactory build up of autumn leaves at the bottom of a small hillock.
Dust-free and private. Actually, probably only private on weekends, but if you don't mind showing off your autumn leaf crunching action to a bunch of desk-bound public servants you could go tomorrow.
Are there public servants in the West Block? Maybe it's the ghosts of public servants from 1927. They would be more used to looking at sheep and British royalty, I guess.
*Don't believe Wikipedia, though. If we called it the ParTri we would be well and truly Looked At. Someone is being a bit TriHard to my thinking.