My guess is the the Company do cover the costs on a shorthaul flight,
Yes, i've done some rough calculations and revised my opinion. I assuming 140m Available Seat km per year, 70% load factors, 20% fuel used on cargo flights, 50% of the remaining fuel (ie 40%) used for the additional weight directly attributable to pax and luggage. Net result is about 1.3p per km per pax. So maybe 5 quid for the typical commuter flight, and less than 10 pounds including everything else.