There is a specific way of hanging it, with the thick white parts of the diagonal cross nearest the flagpole being placed above the thinner white parts.I suppose one could argue that Britain currently IS in distress, and that flying the flag inverted was fully appropriate...
Mr Kearsley said: "Having the flag upside down historically was a sign of distress. You might have it put it up on a fort to warn those in the know - other British forces - that there was trouble from the enemy.
"Forces from other nations wouldn't have noticed. It was like a sort of code."
Details and image credit here.