Ref CJF - You are indeed correct ref the UK law on shotguns, at one time shotguns did not have to be listed, one licence covered all (This is 1960's)

In my ignorance, at the time I smoothbored a SMLE in.303 to.317 ish, it would hit a man target at 100 yards keyholing!! (go to jail nowadays)

Then they had to be listed, proofed for a standard cartridge which is why so many rook rifles were so converted

I cannot recollect double rifles at the time, but recently bought a Purdey in .360 with .410 chambers GRRRR!

TH