As I understand it, as diesel is a heavy fuel it is easier to produce than petrol. So if its easier to produce then it stands to reason that its cheaper to produce. So as diesel is dearer to buy than petrol does that mean they make a bigger profit from every litre of diesel sold?

I've been wondering if its more economic to go back to a petrol engined car.

I've also noticed LPG is slowly creeping up in proce as well.

Diesel is an easier fuel to produce, and it is also cheaper to transport because of its lower flash point making it less volatile. That doesn't escape the fact that the UK exports 40% of the petrol it produces and imports around half of the diesel it produces. I make that 30% or so of our diesel is imported based on government figures, although the RAC stated in 2010 that it was '2 weeks worth' which I make out to be 3.846% imported. So, yes, diesel may well be cheaper to produce, but a large quantity of our diesel will have an international transportation cost added while petrol prices are effectively subsidised by the 40% that we export.

Zunnan, You are wrong about the flash point of diesel, I am sure that diesel does indeed have a high flash point,it needs a high flash point because there is no spark plug ignition. When a tanker delivers diesel to a garage there has to be two people present, which is not required if only delivering petrol. I know that from working at a garage where they were short of fuel stn staff and I had to just stand there for legal reasons.
I have just checked  take a look at this link
http://en.wikipedia.org/wiki/Flash_point

I meant lower risk flashpoint...tireness and phones don't mix! 

Diesel is a much more harmful substance as a biohazard than petrol, needing extra staff to monitor the decanting of diesel won't have much to do with its (lack) of flammability.