There was a piece of footage shown on British TV. Street scene, camera tilted slightly upwards, and something flashes across the screen from top-left to bottom-

There was a piece of footage shown on British TV. Street scene, camera tilted slightly upwards, and something flashes across the screen from top-left to bottom-right. Fast, just a few frames. Never saw it again (admittedly I didn't look very hard). Don't suppose anyone knows what I'm talking about, do they? Would be nice to know it's not a false memory.