The old smooth bored service rifles do turn up still on occasion, as they weren't individually registered back in the day, the owner had a Shot Gun certificate and could acquire what ever they liked .... As a result, when the ban came in some never got handed in. I came across a smooth bore Garandicon (Birmingham Proofed with "SMOOTH" stamped alongside on the barrel from memory) propped up in the corner of someone's living room and covered in thick dust a few years back, the owner inherited the piece from a deceased estate, no one was interested in it and everyone just assumed it had been deactivated!

After a few phone calls, it went to a Sec5 dealer to store and Police check and on to a Sec5 theatre/film prop company from there I hear. (I think they thread the muzzle for a gas restrictor and shoot blanks with such things)
At least it wasn't destroyed, these days it most certainly would be, unless it made it to an official collection.