Hannah_G wrote:I have the day to myself tomorrow and am up for a really diabolical challenge if anyone fancies indulging me

Something I also want to try with my 2 magnetic padlocks - when I have a little more time.
Place a large cardboard box in front of the mirror and tie it so that it cannot be moved.
Put some plastic on the bottom - I'm going to use plastic garbage bags for this - and a mop to catch most of the water.
Put the key to your handcuffs or padlocks in ice cubes.
Take a long stick or a broom handle and tie a magnet to a string at the end.
Now throw the ice cubes with the necessary keys into the box from afar so you don't know where they are in the box.
Tie yourself up on the other side of the room.
The assignment is now to collect your keys with the magnet, but the magnet can't get close enough to the keys because of the ice

. So you will have to wait until the ice has melted enough before you can fish for the keys. This while you constantly see your predicament in the mirror.
If the keys cannot be attracted by a magnet, you can solve this by attaching a number of iron paperclips to the keys.