Oh Ian, a lesson learned I think, get a wireless hard drive and use Time Machine as any electronic device, PC, Mac, tablet etc etc can fail like this....
I personally would do nothing if you can, if I was closer I would swap the HD (if possible) or set it up to boot from an external drive, then hopefully we could get all the data off the drive in your machine. Most decent places, even God forbid the dreaded PCWorld should be able to retrieve everything mate so don't fret if there is anything you really don't want to loose.
But please please from now on back up to Time Machine in some way even cloud and don't store pictures or files you don't want to loose on the same drive as your OS
Edit - above advice very good, maybe Ady can help with another device and thunderbolt cable? He has all the tech know how and is closer to you than any of the rest of us