So you’re driving along the M40, minding your own business, listening to Radio 6, and all of a sudden the cars in front start to brake. Hard.

All the hazards come on, the world seems to shudder for a second, and at that precise moment you look in the rear view mirror and think; oh no, not here, not yet, I’ve got so much more to do before I check out.

And then whumpf-screech-pzzzz, the car you thought was about to pile into the back of you veers left at the last second and wallops the car on your inside. The impact is big but nowhere near as huge as you feared it might be. The people in both cars are quite clearly shaken, but are also perfectly OK.

Before you can even think about what’s just happened, though, the traffic in front starts to move on again, the motorway coughs back into life, and at that point you have a decision to make; move away and carry on as normal, leaving the two drivers to work out what happened and whose fault it is having made their way (you hope) safely to the hard shoulder – or climb out and lend a hand, thereby ensuring that the M40 grinds to a halt completely, and maybe even risk getting run over yourself or, at the very least, cause several more shunts 10 miles further back down the motorway – in order to be a witness to an event that’s already over bar the shouting?