Destruction by overwriting:

When destroying classified material by overwriting, it is recommended to follow the requirements for overwriting and reuse of storage media set out in the National Cyber Security Centre’s guidance Management of the lifecycle of hard drives.

Destruction by shredding:

When destroying classified material by shredding, the requirements for shred sizes for the relevant classification level, as set out in VM 2021:5 Recommendation on the handling of classified documents, must be followed.