I have done some more testing of the servo.
Before starting the car I pressed the pedal numerous times – it was fairly hard and may have become more so.
I then started the car while pressing the pedal and it did indeed move downwards slightly.
I drove the car for a bit and the braking was, as before, abysmal.
Upon reaching the top of my straight, quiet and slightly downhill sloping road I dropped my speed and turned the engine off. I did repeated brake application down the road and the braking got no worse or better. Then restarted the engine, again pedal dropped, and again braking stayed just as bad.
The pipes look ok, assuming these are the right pipes, and I can only see the top of them.