Thanks for your input guys - much appreciated.
Aidan,
It cuts out dead - not like running out of fuel.
Pretty sure no coil suppressor - customer (another garage) has it back now.
Sometimes it restarts - other times no.

Do we not think 'iffy' coil packs and plugs would show up when driving and / or through serial data? There's nothing pointing to them, surely...?

We drove it home on Friday - with the laptop on passenger seat. All sorts of abnomalies were being kicked up - battery voltage 'appearing' to be constant 11V, vehicle 'appearing' to not be running in closed loop. Vehicle did not cut out on 20 min run home. It cut out twice on the return journey the next morning.

We've advised the next course of action should be a test of the ECU. If they do, or I receive any updates, I shall post them.

Wow, sorry for the lengthy essay!
Have a great week,
Andy