Failed rear blind removed from another car, tested in the garage with a spare battery, found to work with power applied to motor and operate fine. Presumed failed relay box to motor. TB had one spare so took the lot up to his where we proceeded to diagnose.... A sticking motor.

I hate intermittent faults, so thanks to TB for sticking with what was hoped to be a 20 minute job that turned into a 4 hour job to swap the motor, which meant the spring loaded gear slipped round which meant taking the little gearbox apart, re locating the spring, re fitting, to find the gear was 360 degrees out and not sprung loaded, remove it again, swap the spring for a non bent one re fit, re adjust gear to line up, re fit again and bingo, perfectly working rear blind , and that's the short story, and then we had to fit it to the car.
Still working beautifully, was playing with it on the way home, even at night in p!ssing rain.
Actually that really was an unpleasant drive home, aquaplaning at 70 on the m40 in shite visibility. It was belting down.