Most solicitors will give you a 30min consultation for free. And £170 per hour is cheap, the trainees at my local solicitors get more than that, iirc the qualified guy gets £300 p/h.

Vez.

At minimum I would call the police, they will either hurry highways up to sort it or send a patrol to inspect.

If you're going legal with it, these are the things I would be thinking about (I am no expert though)

where is the gravel from ?

When did the council last conduct routine maintenance to clear the road?

Has anyone else complained?

Worst case scenario - nobody else complained, they had a sweeper out the day before, unfortunately some random unknown vehicle shed a partial load just before your crash, would the court rule the council responsible?