It became obvious over a couple of weeks of driving, that it was the ABS that was causing the problem... every time the ABS light came on the brakes returned to normal function (this happened often a few minutes into driving - after a dozen or so brake applications complete with sticky pedal, strange grunting sounds etc.). So, I was pretty sure it is not a master cylinder or booster problem. In other words, with the ABS off, the brakes were OK.
Yesterday, I found time to pull the front wheels and pull the front ABS sensors. The ends that face the cog wheel were coated in grey coloured grease. Once I cleaned the ends of the two sensors and reseated them, the problem has disappeared. I am tempting fate a little, but I may have solved this strange malfunction. It does seem odd that a bit of "One Shot" grease could interrupt the ABS signal to the sensors. I'm pretty sure the sensors were fully in place before the "repair."
I'll report back if the problem re-appears but have already received a big kiss and a squeeze from the Mrs...
Could this be another cheap repair?
Pavel