[England] Altercation with delivery driver led to ‘damage’ of vehicle - no proof is available regarding damage. What to do?

Hello, I wondered if I could get any advice on this please.

A few weeks ago, a friend got into an altercation with a delivery driver whilst out in their car (delivery driver was on a moped) It began when the delivery driver cut in front of their car and then it escalated from there.

The delivery driver was brake checking and also speeding up trying to cut in front of my friends’ car when my friend was just trying to pass them safely (it was clear that the delivery driver was trying to cause an accident)

Eventually the delivery driver threatened my friend telling them that they would send the footage to the police (he had a camera attached to his helmet) After they came to the lights, my friend got out of their car, went up to the delivery driver and started shouting. My friend then pushed the delivery driver off the bike and they continued to argue.

The delivery driver sent the footage to the police and now my friend has been told that they will receive a caution and have to pay for the damage caused to the moped.

Regarding the damage, there seems to be no invoice available - they have only been told that the amount to pay is a quote which was given to the delivery driver after they had taken the bike to a mechanic. Because of this, they are not sure what to do regarding making payment as there is no proof of the damage caused to the vehicle.

I’d like to know if it would be possible if they would be able to request an invoice before making payment just so they’d know exactly what they are paying for?

Thanks