Ok,
@andythom188, here goes, apologies that this is in still pictures, but have not got a clue on how to make a youtube "how-to" video, maybe i need a how-to lesson on that.
Lock v unlock.
When it is unlocked the key is very slightly off centre towards the bottom.
When it is locked the key is off centre at the top. (not a good pic, sorry)
Removal.
To remove, firstly pull the release wheel outwards (you can then see the silver coloured centre bar).
Then rotate the wheel clockwise, when the green pin is at the 12 o'clock position, the tow bar will literally drop out, so be ready to catch.
Insertion.
In order to insert it, first pull the release wheel outwards and turn the wheel clockwise till green pin is at 12 o'clock (exact same move as if you were removing it). At this point the wheel will actually lock in this position, and you can let go of the wheel, then simply put the neck in the hole and push rigidly upwards, as it hits home, the wheel will auto lock and the green pin will spin anti clockwise to circa 8o'clock.
At this point you can lock the key and remove it. Your towbar is now secure and can't be removed.