A mate of mine was in a head on crash where the other driver was on the wrong side of the road. Left him very stiff and he still cant lift weights without pain. He has been to various specialists+physio. He has also had to visit an insurance assesor in dartford. The legal team on his own insurance are trying to push the claim forward but its still on going a few months later. I think its normally alot more straight forward then this.
You did the right thing going to A+E as the other insurance company would say why didnt you get medical assistance if you were injured.
Keep a reccord of anything and everything it has cost you, lost time. Events you may have missed and costs you have incurred. Keep reciepts and dont stop complaining until its payed.
If thier offer of compensation is laughable then turn it down but dont be too greedy or overdramatic as it will hurt your claim.