Thanks for your observations and thoughtful comments. The "Japanese connection" was started earlier in this thread with perhaps the most poignant factor being the long serial number on the action flats and the various "look alike" only English marks.
The high quality of the walnut in this sporting weapon, however admittedly does not match the "Japanese copies" of English shotguns. When I wrote to Hamada I simply told them that it had been suggested that this gun was Japanese and if so could he identify the year and the manufacturer - as you can gather from his response - there is simply no clarity on this... I can tell you that this gun (whatever it maybe) leaves absolutely nothing to be desired to a Webley high grade boxlock shotgun. The engraving is certainly all hand executed with tight checkering and the wood to metal fit is outstanding. Here are some photos for comparison to a high grade Webley BLE (alternate Webley first and the shotgun in question):