It's the ammo used. The Brits used 9mm or similar caliber ammunition. Most if not all 3D printed guns fired successfully in the US and Canada used .22LR. Not an ideal caliber for defense, but far better than nothing. The plastics currently in common used simply can't take the pressure of standard hangun calibers. But as a last ditch single shot weapon a .22 is better than nothing.
This video is pure propaganda. Trying to scare off people from printing their own untraceable undetectable guns. Perhaps .22 LR isn't readily available in the UK? But this does not prove these are not viable. Just that the British authorities are so worried about losing control over the serf's abilities to defend themselves that they have taken to making propaganda vids to scare them into remaining helpless.
Guns and ammo are very difficult to get hold of legally in the UK. Even .22LR. In fact, outside of a military base I haven't seen a gun of any kind in the UK for years.
It's possible to get one or two types of gun, like say a double barrel shotgun, but that's about it. It's also a huge pain in the arse to get the necessary permits from the police who also have the right to pull short notice "inspections" of your property where the weapons are stored and often revoke permits on the spot for the silliest little thing that the officer inspecting perceives as "wrong".
