Thanks for all the info.
I gave up trying to delete the data, and took the easier option (as suggested), of changing all my passwords.
One final question.
The laptop is now in the hands of the repair agent, and they've confirmed that the HDD is buggered and will be replaced under warranty.
They have asked me if I wish to upgrade the replacement unit. I would have to pay the difference (about £30) between the original fitted item, and the higher spec unit, and was wondering if I would notice much (any) difference.
The original HDD is 200GB, 4200rpm, with a 8Mb cache
The upgrade is 200GB, 7200rpm 16Mb cache. The data transfer figure is about 40% faster.
I mainly use the laptop for photo editing, word processing, and watching DVD's.