Mike, were the police at the scene?
I assume they were due to the fact there is a van parked in the ditch, but if they weren`t and they did not take a statement from you and the driver then it could be very difficult to get his details out of him.
This happened to me a few years ago, i got reversed into by a luton van and the fella was greek i think, he didnt have his details in the van and said he would pay to get the car fixed without going through the insurance, i felt fine at the time, but as tel says it was a few days later when i was starting to stiffen up, i ended up seeing a physio etc and the car was all twisted too, in short he was very reluctant to give out his details as he had already had 4 accidents that year and because the police were not at the scene they wanted nothing to do with it and would not help me in anyway to get his details