Just drill several holes in the platters of the HDD. or bust them up with a big hammer. Other fun ways: apply the flame from a propane torch to the platters & then scrape the Iron oxide off the platters.
Catapult into the sea after attaching magnets and dousing in tar then lighting,
then go scubadiving and recover it,
drill the screws out and put the platters into a normal cd player, attempt to play track 6, (note it must be track 6 for complete data destruction)
get mad when 'cd' wont play,
run cd player over (with 'disk' still inside) using car/truck (Not motorcycle or pushbike)
put cd player in refuse bin, either wait for weekly collection or fill bin with petrol/similar and light,
wait for fire to die down,
put molten mass through popatim's woodchipper,
eat the shredded chips, no more than two a week though or you will have intestinal issues,
keep the erm, results in a safe place until all has been processed,
pack into flamebricks and burn again (Fire, the great purifier )
Scatter the ashes to the four winds on a Bloodmoon in august
that should be secure enough and next time put 'those' photo's and videos on your phone, not your grannies computer
/wanders off to solve U.K. chav infestation problem....
A format, from what I've seen and heard, doesn't completely safeguard everything. To truly erase a hard drive, you'll need a program like gwscan to write 0's to it. An alternative is to delete absolutely everything on that drive then just fill it up with oversized all-white or all-black true color bitmap images (uncompressed). This is kind of like what gwscan would do, though not as in-depth. If someone does steal the drive and attempt to read the data, instead of seeing financial data, your photos, etc., they'll only see large, blank bitmaps. 20-hour-long WAV files that are nothing but pure silence also works. Just fill up every byte you possibly can. Copy paste helps too.
The 100% absolute solution involves Daemons, Dragons teeth (given willingly), quarry plant and machinery, breaking several (most) US,Nato and Sato guidelines as well as abusing the laws of physics (Sorry Scotty, maybe ye cannae break em but Ahm damn sure ye ken tweak the buggers)
and a vial of virgins blood, although most people will struggle to find virgins blood these days...