You will search in vain for a maker's trade mark on the Graham pair. The last thing the manufacturers wanted the end user to know was who built them. In the event I'm wrong I would v. much like to hear from you.
You can view that exact Lancaster O/U, serial number 13,747, shown on the Guns International site in a photo essay I wrote captions for called "How the Brits Stack Up" which appeared in the July/Aug 1994 issue of SHOOTING SPORTSMAN. In the intervening 28 years since I have learnt nowt about Lancaster O/U's.
If you would like to see the inside of a Lancaster O/U sidelock there's a fair to good illustration (figure 4) on page 157 of Don Masters Atkin Grant & Lang.
Doug
