Yes I know how stupid I've been and will severely chastise myself once this has been resolved.
Just to be clear, I've done a robocopy using the /mir switch and files not present in the source have been deleted from the destination - this was not desired.
I have an exact list of files that have gone, but I have no idea how to get them back.
Unfortunately the source drive was a Linksys EFG80 and the target was a Netgear Stora so I cannot remove the drive(s) and use common recovery utilities as both the units are using some unknown form of RAID.
I would restore from backup, and I believe there is a full backup but due to staffing issues I cannot get the credentials until next week but I could do with restoring this asap before users get in tomorrow.