Hi,
You could try leaving them exposed to sunlight for a long period of time - not a very reliable way of erasing them completely though... And as you're in the UK, it's probably raining anyway! :-)
Sounds like you need a UV EPROM eraser - either
buy one,
buy a kit, or (if you've got deep pockets)
buy one pre-built. Failing that, there are
plenty on the UK eBay at cheap prices...
- Ali
