I've always wondered about that, I'm probably being daft asking the question, but would a little bit of petrol mixed in cause as bad an effect on the engine as trying to run it on full on unleaded?
No a little bit of petrol mixed in will cause no issues, it used to be a common thing to do in the winter months, stick in a bit of unleaded with a full tank of diesel to
lower the flashpoint and aid starting among other things
It even used to recommend doing it in the owners manual of my 5 series bmw
Although with modern diesels it is probably not needed or recommend, especially on a regular basis