Jet A1 is a cleaner version of keroscene. keroscene is pariffin. Pariffin is cheaper than diesel by along shot (Is it still?)
You car will run of parrifin and probably of JetA1. Doubt for long though. As Rich said, no (Little) lubricants in the fuel.
A lot of dodgy stations dilute diesel with paraffin to reduce the cost because pariffin is not taxed.
As Rich said, that is breaking the law. Tax evation.
There is a lot of that in the UK where they use famr diesel (Lower tax, lower quality) for cars. Constanty getting nailed by it.
Did he say what bakkies they are? 1912 Hilux or Landrover? 
Those can almost run of crude oil.
Cheers,
Crispin