Ray of hope! You say 'a large van'. Is this Transit sized or bigger, like a 7.5T truck? If it is over 7.5T it requires an operators licence. If so, it should be in the window by the tax disc (like a tax disc, but probably orange or blue, though it could be white or green...thats VOSA for you!). In this case he must 'normally' park at an operating centre. Take the number off the disc (like OF 123456) and report to the Police or your local VOSA office (in the phone book). If it is Transit sized, I'm afraid like Ethel says, you will be struggling.