@Mac – many thanks Mac, will turn off AV and disable Internet connection next time round / yes, I should have defragged first.

@John – thanks John. I was operating at normal compression. So ideally I would need a spare PC to test the backup images. (Isn't that a problem with the software licenses - notably the MS ones, which must know that they are being put back on to a different PC?)
That makes sense, but I don’t have one at the moment. Will have to wait until my next PC purchase.
I would be happy to buy the full version of ATI, but do you know if I could use it on more than one machine?

@Gary – no, it was a USB 2.0 connection, but I think you could be onto something. The drive was plugged into the PC via a USB hub, which is probably not the ideal setup. Another factor for me to correct next time round.