does your aunt work for mi5?
if not ... either bite the bullet and erase the disc
http://www.heidi.ie/eraser/faq.php#erase hd
once you've made the disc ...
http://sourceforge.net/projects/dban/
just leave it running ... not hard
or delete everything reformat - take it out bung it in the shed or garage in an old shoe box ... if it reacts like my garden tools ... it will be destroyed and useless within a couple of weeks.
as marky says ... it won't actually get rid of the info - but if the disc lives in the garage it's unlikely to fall into the hands of international mafia techno fraudsters.
I suppose the best alternative is Ethel's (also marky's)
caddy suggestion
(although why a golfer's assistant would need a HDD escapes me!!)