Okay, call me a stickler but if your gonna hang it, do it right. The union jack can be rotated and it will still be the correct way up, but it cannot be inverted as it is not a reflective symmetry.
Take note of the white diagonals: the wider white diagonals should be above the red on the side that fixes to the hoist, pole, bunting...
Flying the flag upside down is a signal to indicate 'distress', it is also insulting the crown, which in theory is still a crime in the UK.
Have fun this Jubilee weekend and fly your jacks with pride.