Update - Frequency of the 'problem' on my one increased.

Identified as the starter motor clutch. New starter fitted and problem solved.

That would be my best bet too - something at the starter motor .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Also check the battery lead clamps on the battery. Check if they are loose and check for corrosion on the clamps/poles. Clean the inside of the clamps (fine sandpaper and cloth) and the outside of the poles and put a thin layer of vaseline on it (to prevent future corrosion). Check all the earth connections, especially the bigger ones, take them off, clean them and put them back with some contact cleaner or the likes to prevent corrosion. A little resistance with 12 Volts can cause a big voltage drop. MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!