We are OAPs (that places us in the almost idiot class to some!) On Saturday my wife put £5.00s worth of Sainsbury's City Diesel in the petrol tank of her 2004 Daihatsu Charade - because the fuel warning light was showing.

She did NOT tell me that she had done this but just put the car away in its garage and asked me to fill the Charade's tank (a usual task) which was almost empty.

When I came to take her car the next morning to fill the tank (Shell V Power - always used in both our cars) it started but ran very roughly indeed and I had a struggle to keep it "alive."

However, it finally ran smoothly and I took it to Shell Peacehaven and brimmed the tank with VPower petrol. No starting or running problems but on return home when I spoke to her about the rough running and the probable need to have the engine/electrics/fuel system checked in advance of the June annual service she confessed to her mistake!

I assume that the diesel is floating on top of the petrol and it will stay that way until the level falls to the point where it is pumped through to the injectors?