Hey guys,
Just worked out that following my email from GAME UK requiring me to create an Elderscrolls Online account, it is not correct!!
You need to use the code provided in Steam to download/pre-download the game.
It does not work if you try to redeem the code at Elderscrolls Online.
Bit annoying, but since I already had both a Steam account and ESO account it wasn't too much trouble for me - Here's hoping I save someone else a bit of time!!