Klara the car does strange things that Fleur never thought of. One of these is to beep when she's running out of petrol. Fleur used just to stop. It's probably an advantage but it is rather worrying. What if that beep means she's about to run out NOW?
So when she beeped on the motorway I decided it wouldn't be safe to wait 23 miles until the next service station and came off at the next junction and ventured into Slough to find a garage. I did eventually find one and it may have taken less petrol to do so than continuing on the 23 miles, but John Betjeman had a point about Slough.