Procedure for suspected bad fuel

[T3rminator]

What is the normal procedure if you suspect you have filled up a tank with bad fuel?

Last weekend we filled up mum's Kia Sorento (Diesel) at the local BP. Car started fine after filling. Drove half way to Geelong and stopped over for a coffee. Got back in the car, went to start it, and it just kept cranking but not firing up. I turned the car off, and tried again, again extended cranking, then finally started. Car drove fine but sounded a bit noisey at low RPMs in 1st and 2nd gear. The car has been like this since.

I told the folks to go to a reputable mechanic shop and get them to submit a fuel analysis. For some reason, dad didn't want to do that. Instead he called his mechanic mate who came over and ran some diagnostics via the ODB2 port. Not sure what software was used, but it cleared up the car a little and started ok that evening. Next morning, extended cranking again. I told dad to go get some fuel pumped up and tested by a shop, again he ignored me, and instead bought a bottle of Fuel Dr and put it in. Its been 2 days since Fuel Dr, its running slightly better, less extended cranking but still not normal. And on morning start ups, it emits a lot of smoke for the first couple of minutes.

He is now asking me to call BP........I'm banging my head against a brick wall as I doubt they will accept a fuel test now.