Here's a 1924 Vicker's Reprint(maybe one of the 1st years of Vicker's Sporting offerings??) at Cornell Pubs:

http://www.cornellpubs.com/old-guns/item_desc.php?item_id=769

So with the Crayford history and the 1924 catalogue(looks like Crayford-North Kent was the sporting weapons manufacturing facilities), and considering the Crayford facility was closed in the late 1920s, if only for a time, this might date the longarm between 1921 and say 1927?? That is if Crayford was the only facility churning out sporting guns or if stooped to sourcing weapons with their name roll stamped on them.

Kind Regards,

Raimey
rse