[Enfield-Stuff]

The .22 caliber adaptors were built and marketed by Parker-Hale, patented 17 January 1923, "supplied in quantities to the Canadian Defence Department, the Small Arms School Pachmarchi, India and the Government of Northern Ireland. By 1940 is was also available for use with the caliber .38 Enfield Service Revolver and the .38 Webley Mark IV. (pg. 232, Webley Revolvers, Bruce & Reinhart, 1988.)

Pretty scarce, actually. The kit was intended to temporarily replace the regular cylinder for economical target practice. So the revolver up on auction is "missing" the original cylinder.

 

[Enfield-Stuff]

I did a fast skim of all of my Webley books. If looks like P-H did conversion kits for both 4" and 6" barreled revolvers. Interestingly, I have one that will fit either - the tube extension simply threads into the shorter tube. Webley did do a single-shot mono-block conversion kit, which I presume was for Webley pistols. The 1945 Parker-Hale catalog has an array of .22 caliber training devices, including one for the 2-PDR artillery, the Boyd anti-tank rifle, the Vickers Machine Gun and the Lewis Machine Gun.

(Note: pop over to Cornell Publications They have reprints of many old gun catalogs. There is an amazing amount of information to be found for very few $$.)

I've seen the Parker-Hale Webley conversion kits go for $400 - $1200. Revolver not included.