I admit that our firearms legislation is not very good, however, your comment doesn't make sense. There are many people in the UK who own firearms, unfortunately you have to jump through many hoops to obtain a firearms or shotgun license.They would just turn them in along with their steak knives.
And cars
Basically a shotgun is a smoothbore with a maximum of three cartridges (two in the magazine and one in the chamber), whereas a firearm has a rifled barrel (i.e. a rifle), or a shotgun with a magazine capacity greater than described above. The only self-loading firearms (semi auto as you would describe them) we are allowed to own are .22RF and shotguns. There are also many other nuances in fact too many to describe here.
Enjoy have you have in the USA and I hope that the looney left don't try to overturn your 2A rights.