I can't say if it was done in England. I have done some in the days when I worked on Mausers.
(I do only muzzleloaders these days)
It's not all that hard to do, but it takes a lot of time.
The "secret" is to draw it out in 1-1 scale on paper. Take pains and get it drawn perfectly.
Keep in mind it has to be shaped so it can go into the wood "straight down" as that's how the action has to go in.

Weld up your extension and bend and shape it to overlay your drawing perfectly. Again, get it as perfect as you can. Take time with your files and get it right.
Inlet it into the wood next.

(note....You inlet the action first, so you have a mortis for it to go in BEFORE you extend the tang. The extended tang is done as an "add on" so you have everything done in the inletting of the action before you start work on the tang.)

Once you have the tang inlet you file wood and metal together for a perfect fit on the surface.
Now, the last thing you do is cut the slot for the safety and make the button. When it's done you polish everything up to 400 grit, wood and metal together.
You then need only make a heavy spring wire bar to attach to the safety of the trigger and inlet the wire and clearance for the button under your new long tang.
Presto.......custom look with tang safety, ready to blue and engrave.