The car is left overnight, like normal.
It's started in the morning to go to work and the brakes need a massive effort to stop the car. Same as a non servo assisted car: if anyone's ever driven an early Mini, with no servo & drums all around, you'll know what I mean.
This only happens for the first few hundred metres/less than a minute of driving. Afterwards, the brakes operate normally. I've tried the car and the brakes feel perfectly good (for a 106 of this type) so the servo must be working by this stage. Yet initially, they're awful.
Master cylinder is new.
Front pads are new.
Rear cylinders are new.
Rear shoes are new.
Fluid is new, twice. No air.
One caliper is new.
Vacuum hose *seems* OK: not perished/cracked etc. Could it be just the seals?
Is it likely that the pump has failed? Remember that the car has normal-feeling brakes just 200 metres down the road...
Is it the servo that's losing air slowly while stood overnight, and taking a minute to build up it's vacuum after the car's just started?
After the initial bite has come back to the brakes, they work fine for the rest of the day: even after the car's been turned off. Even after a normal 8-odd hour stint in the office car park twiddling its thumbs/wheels, it's fine.
When sat overnight (more like 10 to 12 hours), all is not fine.