Quick Rant/ Q for you fine lot 'what would you do'

Tell him you know it was his doing and ask if he wants to get it fixed or go through his insurance

We can't just go hiring people's cars and expect nothing to be done about it

Bill

As above, and see if he says he'll pay cash. How bad is it?

Take pictures, phone your insurance company and screw the careless curse word over

Get him to pay then a public hanging in the car park

^^^^ as above making sure to get GOOD pictures of both the damage and your paint on their vehicle, then make sure you get any CCTV before it gets wiped, I would approach the other person to and ask them what they are going to do about it as if they don't offer to sort it themselves you'll put it in the hands of your insurers who will them proceed to screw them good and proper.....

Bummer, this isn't looking good.

You could advise him that you're passing the allegation, along with your evidence (the details of which you must remain silent on to avoid telling lies), to your insurance company. Suggest that he should not directly contact you again on this matter.
A huge bluff is really your only option given the lack of evidence and quick work on his part.

i would be going to see if theres any cctv in the said carpark and asking for a look at this but also recording it on a mobile(just to be sure you got a copy even if refused to be giving it)
if it shows the incedent. also saying that the reason you ask is to clear the matter up without any hassle between work colleages and any bitterness, if he has mentioned insurance also tell them you would rather let the bloke pay less to repair car without letting him pay excess and having a claim against his name which will cost him more in insurance in future years.

My tuppence.

You knew who it was - Why on earth did you send an email?

You should have gone and spoken to him face to face. Most reasonable people wouldn't have done it deliberately - He may even believe he genuinely didn't do any damage to your car (or may not even have noticed his door touch your car?).

If you'd have gone and spoken to him in an adult-to-adult way I believe you would be far more likely to have got the outcome you wanted. People tend to be more reasonable when you take things up to them in a polite, objective matter face-to-face I find - You could have said something along the lines of "sorry mate, I'm not messing about here, come out and take a look for yourself", then shown him the evidence. His reaction to this would tell you all you need to know.

Call me naive but in such situations I always assume people are adults who are on the whole fair, so I treat them as such.

Sorry if this isn't what you want to hear.

Jolly good, let us know how this goes.
An invoice for my legal advice is in the post along with a certified copy of my law degree from the University of Google. ;D