Success!
I've managed to slip the timing chain back to its original position. It only took me 4 hours of trial and error but I've now perfected the art of chain slipping
I used a piece of flexible plastic to slide down the chain so that I could separate the chain from the crankshaft sprocket. I then turned the camshaft back to where it was supposed to be and the chain slipped easily over my plastic "chain slipper tool".
I can't take credit for the idea though.....I seem to recall some other pelicanhead suggesting this in a previous thread
Thanks for all your help!