Update:
It was the low pressure (in tank) fuel pump. Apparently the fault shown was a short circuit but they replaced the pump (took weeks to get one) and that problem has gone away.
I hadn't updated here as I threatened to reject the car as it had so many other faults, but the dealer agreed to repair everything:
Front lower suspension arm (bad tracking)
Front stabiliser bars x 2 (rattling over bumps)
New battery (would not hold charge)
2 x wheel bearings (left side) - terrible road noise
New aux belt and tensioner - rumbling
New front discs and pads - vibrating
I still needs a wheel bearing on the right side, there is a strange grumbling when coming off the throttle from the air intake in the wing, the GPS aerial is dead (no Sat Nav and it's 2016 apparently) and the wheel alignment is off. But I'm a bit bored now. Anyone want to swap for a D4?
Also - the ride is terrible - side to side rocking - never a problem on the D4.

to prevent depression!