And how would you have reacted had you spun on the road and crashed due to it not having been gritted?.

As for the grit itself, yes there are stones in there, but very very small. I think it much more likely that it was a stone thrown up by the truck tyre that has done the damage. I live in North East Scotland and most of the roads i drive on are single carriageway A and B roads. I often pass gritters heading in the opposite direction so the speed the grit is hitting my van considerably higher than when you are overtaking one on a motorway or dual carriageway in the same direction, but i have never had any problems.

On a motorway if you don't want the risk of damage, it might be best to follow the gritter at a decent distance, keeping to the inside lane and a long way back so others can pass if they so wish, the gritter is usually in the middle lane so lorries will want to overtake on the inside, so would be best if you don't make a rolling roadblock by making it impossible for lorries to pass you then undertake the gritter.

Nine times out of ten the gritter will exit at the next junction even if its to go around the roundabout fully and rejoin, thats when you get back up to speed, you will probably lose 2 minutes in all.

In some other countries they make do without salt, Japan for instance, though i have no idea what sort of product they put down instead.

I'd like to see the end of road salting, our cars would last decades longer than currently and our vehicles and roads would be so uterly filthy for months on end.