Okay, I can now more accurately describe my brake problem!
I have been driving about today, taking care not to abuse my new brakes.
After driving for a bit without using the brakes, when I press the brake pedal, the pedal almost gets to the floor, poor brake response and poor braking generally. If I step off the brakes, and then re-apply the pedal goes less far, the brakes bite much better if I do the same again, the brake pedal travel is as it was, and performance is good. However, a few moments of regular drivinbg later, and the whole cycle begins again.
It isn't the brake disc coating as this would give the same performance irrespective of the number of presses.
It is almost like the pedal felt after the brakes were first replaced, and the fluid needed to puch the new pads up to the discs after being replaced. Do 156 calipers have a non-return valve of some sort which I have broken?
Any ideas gratefully received!!!