I am normally the most cautious of the cautious, BOAC! I'm not going to use the old drive for anything because it has some bad sectors and is also starting to get a little noisier than before. Security isn't really an issue because it's sitting two inches away from the new functioning one whose data is already more valid and rather easier to steal - and without the need for a screwdriver too!!
When the time finally comes I will smash it to bits and steal its magnet!!
Thank you for your interest and advice.