Hello, my name is ***** ***** I will try help you with this.
This depends on how much fuel was in the tank before you added the petrol and also if you have either turned ignition on or started the engine.
If the tank was say virtually empty before you refuelled or the ignition has been switched on after then you should have the system completely drained and refilled.
If it was empty but the ignition has not been switched on , then filling completely with diesel should be ok. You should also keep the tank full by adding more fuel every 50 miles or so.
The important thing is to know that mostly petrol has gone through the high pressure pump as this can cause problems, so if the tank was low and the ignition has been switched on or engine started then you need to drain the system.
Thanks. I came to the same conclusion based on quick internet research. They say less than 5% is ok. I had not swirtched on the negine. Just waited and checked the internet. Then filled up with diesel to the maximum and set off. But your answer will put my mind at ease, thank you.