Go through his insurance - the end.
Fixed.
Your insurance will likely go 'whatever' and leave you to do all the legwork claiming off him (in my experience...) apart from getting whatever ambulance-chaser solicitors they're in cahoots with to send you letters saying "tell us if you have whiplash!!!"
You're claiming off his insurance, not your insurance. Do you have his car registration details and his insurance details?
If not, alarm bells are ringing loudly.
IIRC you have 24 hours to report a collision to the police. IMVHO you should...:
- ring Renault NOW and ask for a ballpark quote for all of the parts listed, without labour or painting or fitting, and then workshop book hours (and rates per hour) to paint and replace them (ignoring the boot floor issue for now). If you are local to a Renault showroom, you could even drive over and wander round the back to speak to the workshop chaps direct rather than relying on the shark-like sales guys in the showroom to relay the message and take ages getting back to you.
- Do some quick Autotrader trawling NOW to identify like-for-like (condition, mileage, service history, colour if rare) replacement costs of a whole new car.
- Contact him (in writing, for future audit trail) immediately to give him both the Renault costs without the boot floor (which will likely be £2k+, as already mentioned) and the Autotrader like-for-like prices, to show the stupidly high repair costs and therefore the likelyhood of write off and the expected cost implications associated with that. State that on the basis of the evidence presented, you must therefore seek the full replacement cost of the vehicle in cash or bank transfer [to a rarely used account with nothing in it!] if he does not wish to go through insurance.
- In your contact, ask him to confirm receipt of your message by return email/text message, and ask him to confirm or reject your preferred resolution of the full replacement value. State that you are giving him until 30 minutes before the time the accident occured yesterday to respond because you need to report it to the police within 24 hours.
- if he does respond by calling you, email/text him with the agreed resolution (or the current position if no resolution) after the call has finished (for audit trail purposes).
- if he responds by text, take a screenshot of the conversation and email it to yourself in case it gets deleted by accident.
- if he does not respond by the deadline, text him at that time to say that it appeasrs the deadline has been missed and you need to ring to report the collision to the police in 10 minutes.
- if that doesn't result in a response, get calling the old bill. And his insurers, if you have the details.
TBH, even if he does text and confirm he is happy to pay £5k in cash (or whatever) I think I'd still call the police to report the collision. That way it's recorded and you have something to wave at him if he dicks you about coughing up the cash.