Cement Seal, French Portland, Image & Found by Ben Bennatto.
Found in Cornwall, 15mm.
From the finder, "It is a french cement bag seal it should read on the front "PORTLAND DEMARLE LONQUETY" and the reverse is "CIMENTS FRANCAIS BOULONGE SUR MER" I have attached some better pictures that blow up better also i have put a link to a similar seal I found on the net. The original national french cement company was formed in 1881 and is still around in the form of Ciments Francais on google."