Sorry, Daz, no!
There are ways to free a 'frozen clutch', where the disused clutch plate has rusted to the flywheel, but it sounds as if your master cylinder has seized.
If it's that seized, then a rebuild may require sleeving to restore a smooth enough bore, that will cost more than a new one. See: https://rimmerbros.com/Item--i-GRID007803
John
PS Johny, among the 2001 uses of WD40, that of penetrating oil is not one of them! Daz might try with a properly designed product. I've had success (not with brake cylinders) with Innotec Deblock X5.