Good observations, all. It is a Purdey and is for sale at Watson Bros. in London. Their website has a few more pictures. I also note that it is marked "choke", which would either mean that the original barrels were jug-choked at a later time or as Dr. Drew proposes, it was rebarreled in the "choke era".

As for the Damascus pattern, I believe you ID'd my 1871 Boss a few weeks ago with the same type of 4-iron Turkish, so perhaps a contemporaneous material corroboration?

Owen