I came up behind a fairly new M4 on one of my favourite twisty 60mph limit roads. The driver only seemed to want to drive at 30mph and couldn't avoid crossing the centre line at corners so I resigned to have to just follow him. When we reached the end of the road and turned onto a stretch of straight 40mph limit road, the driver floored it and (I guess) exceeded the limit by a big margin. Why would a driver behave like that? Of course I eventually caught up with him when we had to follow other cars doing 30mph.