As you say, the intermittent nature of the problem doesn't point to the battery. Especially if the engine starts after 8-10 seconds of cranking; a weak battery would no longer be able to start the car at that point.
That said I'm not sure what else to suggest. It's not an immobiliser issue since the car starts eventually if you continue cranking over. Fuel pressure seems likely, although without other symptoms (noisy pumps, running on after ignition is switched off, hesitating/cutting out under high load, consistently requiring extended cranking to start, etc) I'd be looking at the control system rather than mechanical components. Perhaps have a check of the fuel (brown) relay and the wiring to the plug, see if there are signs of arcing around the pins or any damaged wires. Could also be a failing cam or crank sensor.
That said I'm not sure what else to suggest. It's not an immobiliser issue since the car starts eventually if you continue cranking over. Fuel pressure seems likely, although without other symptoms (noisy pumps, running on after ignition is switched off, hesitating/cutting out under high load, consistently requiring extended cranking to start, etc) I'd be looking at the control system rather than mechanical components. Perhaps have a check of the fuel (brown) relay and the wiring to the plug, see if there are signs of arcing around the pins or any damaged wires. Could also be a failing cam or crank sensor.
