It seems to fit, so hopefully it was made for the Lanchester. Admittedly it doesn't look Britishmade. It may have to remain a mystery...
---------- Post added at 09:51 PM ---------- Previous post was at 09:46 PM ----------
Thanks. Unfortunately I can't give it a full test as the barrel is welded into the receiver. As for the patina, I suspect some bored Egyptian army recruit in the 50's or 60's cleaned it to with an inch of it's life - taking almost all the finish off the metal. However, they didn't bother with the finish under the woodwork so hopefully it's original.