Ok, this helps.
Here is what I did to engage with him:
1. Had Porsche perform an estimate of the repairs and cost. Left the estimate on his windshield with a nice note asking him to discuss the matter with me.
2. He replied to me by e-mail, as follows:
Hi Jerome,I saw attached to my windshield today a bill for over gbp 2.3k for some extensive repairs to your car. I'm very surprised by this letter. I have never hit or scratched your car. You can see from my car that there are absolutely no marks on it - something that would be impossible given what is written in your invoice.
All that said, if you had any suspicion you should in any case showed me what you think is the alleged damage before deciding to repaint your car ask me to pay for it. I will, for the record, take detailed photographic evidence of my car as proof that there is absolutely no dents or scratches, which will act as proof that whatever alleged damage there was on your car could not have been done by mine. I'm happy to show you the photos. However, as you know where my car is parked please feel free to inspect yourself.Regards,Axxx
3. I replied to him by e-mail:
Look Axxx, we discussed this person to person a few month ago. When we discussed this, you absolutely agreed at the time, that the dents on my panel and left door at the time two dents) were caused by you opening your door and because of the little space to do so. Do you remember? You said and agreed that I would get this repaired and you would then pay for it. Have you changed your mind?