Some diesel cars can run on a vegetable oil/diesel mix as much as 50/50. My mate ran his bedford midi on 50/50 mix with no problems. I heard the Lucas diesel pumps cant cope with the mixing of veg oil an diesel and can do the pump in.
I also did the petrol in the diesel thing a few years ago,i put about a gallon of petrol in before i realised,i just filled the tank with diesel(i could aford to then lol)and all was fine
I know F all about cars so forgive me if I am talking out of my **** :full, but wasn't that a reccomended practice anyway in the early days of diesels, put a gallon of petrol in the mix, during the winter to help stop it freezing??