That's amazing info thank you!
I ended up just making a macro to popup the Clipboard History switcher so I can select what ever I want and delete it.
Many thanks, Andrew
If you haven't already, take a look in the Macro Library (Window->Macro Library or ⌘2 when in the KM Editor) to see some useful macros you can easily add to your setup -- including, in the "Clipboards" section, the "Activate Clipboard History Switcher" macro.