As I said in my disclaimer, I don't advise anyone to do this in a car they like. I stated 5% based on a "safe-ish" estimate given the advice I received. This was that for 10 litres of unleaded in an empty tank, filling up with a further 70 litres (approx, please don't tell me my tank will only hold 78 litres) of diesel would be ok. It
was ok, and I would use diesel with a small amount of petrol in my volkwagon again if I had too.
I did say that I didn't really like this car much, didn't I
Also, the petrol should float on top of the diesel (shouldn't it?) and will evaporate off in time, which is why I kept the tank topped up for a while after it happened. Therefore the chance of any appreciable amount of petrol going through the pump or injectors should be slim.