I think that it's the denial that is seeing this go to court.
I'm guessing that his neighbour's insurance company is unable to recoup money from your friend's insurance company because your friend has refused liability.
That's why it's going to court.
I have no idea how your friend will stand with regard to his insurance company as regards that situation.
I would contact the insurance company before the solicitor's letter, myself.
What if the insurance company refuse to cover court costs?
If your friend loses, he becomes liable for his neighbour's legal fees, in addition to anything else.
What if his insurance doesn't cover that?
If it was his insurance company refusing liability - without instruction by him - I think it would be a different situation.
He needs to get this very clear with his insurance company.
Because it sounds very much as though he has been the one to deny liability. Is that the case?