You'll find that Boswell's have a London address and Birmingham proofs. From what I have read Boswell did not get along with the man who ran the London proof house and had his guns proofed in Birmingham.

Everything I have read has said Boswell guns are well made. I have a Boswell hammergun w/under lever and I think the Lancaster tilt and drop action. It looks like a Jones under lever but the barrels move forward before dropping.

I have become addicted to English hammered shotguns to the detriment of my wallet.