Well Motorworks did have one second hand that I ordered for £50.
I was a little suspicious when it arrived in a package not much bigger than a shoe box!
Opened it to discover it had turned into a battery
Phoned Motorworks up and they said they would wait for the guy with the pannier shaped battery to phone them. He never did
Ended up buying the individual bits that I damaged when I tried surfing down the road on my left pannier.