Seeing the two threads by Ken Maddock, with both guns showing Irish numbers reminded me that the Irish Law (see here
http://www.gunpolicy.org/firearms/region/cp/ireland ) under "Marking and Tracing", requires, and has for many years required that ALL guns including antiques be stamped with individual registration numbers. These numbers do not relate in any way to makers numbers.
Over the years I have seen several similar stampings on ex Irish owned antique guns which had eventually found their way to this country.
Stu