Thanks for the replies so far.

In summary:
Trouble with crank sensor connector, about to change this.
Engine sometimes momentarily cuts out at low revs, then continues OK.
Engine sometimes cuts out with flashing glow plug light, recycle ignition switch and it will restart.
The start-up trick noted above reads low battery voltage, although battery is really OK.

Not sure which of these is interrelated, so need some more detailed fault data from an OBD scanner.

See my other thread, does anyone have the ECU pinouts for this model ?