It might not be a case of hit and run, depending on the circs and no one was about who claimed to own the vehicle or know the vehicle's owner personally, however in such circs i would have left a note with contact details under the wiper blade...could the chap have done so and either the note was blown away or removed by someone else?

Either way, it's an insurance claim assuming your witness will give a statement unless the chap turns up out of the blue shortly with £ notes in his sweaty mitt to sort the job out.

If a person has an accident they have to exchange details with the other party. If they can't do so, they are obliged to report the accident to a police station AS SOON AS REASONABLY PRACTICABLE and in any case within 24 hours. If they fail to do that they commit an offence which carries 5-10 points (and theoretically prison). The police will prosecute if they are provided with reliable evidence. In your case, it's only a mirror that was already broken and you are not a witness, your friend is the only witness. I think on this occasion I would agree with Driver since 1988 but with less certainty than he professes.

As far as what compensation you are entitled to, it is negligence, so you are entitled to be put back in the position you would have been in had the negligent act not occurred.

In other words a deduction for the fact your mirror was already broken.

Your insurance would record your claim, even though not your fault.

Sorry. Forget it. Fix it yourself.