If you have a LOT of gear - ie. rooms full of the stuff as I found in a hoarder family home I had to clear recently you can pay £200 to have a professional IT recycling company to take it all and wipe all the disks on your behalf. They provided certificates for all wiped hard drives and recycled items.
Freecycle is also good as are forums like: https://forums.servethehome.com/
If you have a LOT of gear - ie. rooms full of the stuff as I found in a hoarder family home I had to clear recently you can pay £200 to have a professional IT recycling company to take it all and wipe all the disks on your behalf. They provided certificates for all wiped hard drives and recycled items.