Thanks to both of you for your replies. I should have made it clear that I wanted a static EHD because we only use our computers at home. Having read your replies and thought about it a bit, I realised I could buy an Apple Time Machine with a discount via my University account, so I had a look at the reviews. We're talking £250 plus and the reviews were dreadful, the main problem being the internal power supply. So I've gone with my own experience, having had two LaCie drives without a problem for some time, and ordered a LaCie 2TB.
Thanks again.