Several weeks ago, I accidentally put 20 litres of unleaded into my 9 year old, 93,000 mile 1.9D Renault Kangoo. I immediately filled the rest of the tank with diesel (about 35 litres) and ran the car as normal, squeezing in 5 or 10 litres of diesel at every opportunity in order to "dilute" the petrol. Starting from cold was more difficult than normal, although the engine seemed somewhat smoother running, especially up to 40mph, than when just running on pure diesel. The tickover was erratic until I had put some 20 litres or so of diesel into the tank and once I had done about 500 miles, all problems disappeared as I was back to just diesel in the tank. Now, some 1000 miles later, it runs perfectly, with no hint of any problem. When I was an HGV driver in the 1970s, it was standard practice to put petrol in with the diesel to stop the diesel "waxing" in below-zero conditions and blocking the injectors.