Once, flying a PA28 cross-country East-West through the "corridor" -- the space between LHR and LGW -- with London Info on the box, something small, fast and Ferrari-red that looked like a Falco shot up from underneath dead ahead of me just outside a distance that I would call a near miss.
Had he seen me at all before starting his manoever? I was above and behind, maybe the worst place to be conspicuous. But still... the corridor is a very busy place. If you absolutely must block it with an aerobatics box, it's not the cleverest idea to keep radio silence about it.