Some more info may help decide the issue: The driver states the car started to cut out, he looked down, noticed the high temp gauge and pulled onto the hard shoulder. He left it to cool for a while then removed the rad cap to help stop it boiling up. Then he drove it the rest of the way to work. My estimate is he drove for about 20-25 minutes from cold before the problem, the last 15 being on the motorway. And a further 10-15 minutes to get him to work. So no low battery and no problems with injector pump - which I'm guessing is chain driven anyway - or it just wouldnt run.

My opinion is that the engine was 'picking up' due to overheating. I do think it would be handy if the motor DID cut out to save you wrecking it - rather than giving you a low coolant warning after it seized