While booted from the local Recovery, you most likely will be blocked from erasing the root physical disk.  That Recovery is a hidden container or volume on that drive.  It can't delete a disk, volume, container that is in use.

Depending on the version of macOS, you could try to select either a container or volume on the physical disk and erase that.

For best results to ensure a full erase, you'll either need to boot the Mac from an external source or boot it up using Internet Recovery.  That will allow an erase of the entire physical disk.

@ukmercenary Is there a volume named "Update" showing in Disk Utility? If so, you have to delete it (select it then click the Volume "-" button) before you can erase the drive. I'd recommend deleting the Macintosh HD volume as well, and if you see an option to delete the Volume Group when deleting Macintosh HD that is the option you'll want to select. Once those volumes are deleted the normal Erase button should work.

Brilliant ok will get when I’m next back in office next week.