Thank you for updating the thread, LE.
I don’t remember seeing these two before.
Centrefire automatic suppressed submachine gun - Sterling L2A3 Experimental (about 1958) - Royal Armouries collections
Centrefire automatic submachine gun - Sterling Patchett (L2A3) Experimental SV (Silent version) (about 1965) - Royal Armouries collections
Looks like they were made using Fazakerley guns.