Well I've decided I can't be arsed wasting any more time trying to recover the data off it - so now I'm low level formatting the beast before sending it back to the people who I got it from, so that I can get a replacement.
Maaaan, it's taking ages... it's just gone over 10% of the way through the drive and has taken about an hour and a half... and I wanted to post it today... oh well!