My guess is that because it's Great Britan (UK), they allow these although not to practical but functional. This probably is to make sure no one conceals and handguns as the minum barrel length is 12".
It does appear that the 12" model does have a wire stock of some kind. I personally would not want one of these, as I don't feel they would serve a purpose. The 12" model would see some range time, but the 22" model would be to blasted heavy.
Makes me wonder why noone's made a revolving rifle in modern cartridges...or carbine....saw a huge old black-powder-looking thing in El Dorado....what'd it be like in .357 or .44-swing-out cylinder and 18" barrel....hmmmm
Yeah, but you paid your dues to get here...I like onions/eggs/cheese...I like bread&butter pickles/eggs....I just like eggs/eggs....even with a bit of Pace med. salsa thrown in...and milk to fluff them up...gotta go eat breakfast...'bout to ruin the keyboard droolin'....