Nice one Gareth,
I have been driving a diesel for nearly twenty years. In the early days the assistant, at the pumps, would warn you that you were about to put diesel into your car (when you could find a garage selling diesel). Nowadays many, many more people use diesel after having been using petrol for years. I have now passed on your advice to all of my friends and family. I didn't want to have to say that I already knew how to prevent it, if it ever happens to them.
What a great forum!