Very, very true.
After the hearing, NCA deputy director for investigations Chris
Farrimond said: "It is the first time that a fully-functioning firearms factory creating firearms from scratch has been discovered, to our
knowledge, in the UK.
"It was producing handguns, copies of a
Browning pistol, from absolute scratch - from the nuts and bolts and
producing fully functioning lethal firearms at the other end of it, with
the bullets to go with it."
No way of telling whether they were actually manufacturing ammo, or reloading cases, but either is possible.
I'll bet there are others. I've read that during WWII Sten subguns were produced in bicycle shops in the UK, so making something similar now wouldn't be difficult. But they still think they can make them go away...
There's a site called Impro Guns that tracks information about such, the post links notes
that this guy did manufacture the ammo for at least one of the guns he made.