2001 ford transit excessive fuel use?

Hi. I used to get around 32mpg on my 2.0 fwd t280 when unloaded. Now I have been carrying 500 kg in the back and my fuel consumption has gone down to around 10mpg. I just used a nearly quarter of a tank (£25 )on a 40 mile trip. Does anyone have any suggestions why it's doing this? I only plod on at 55 and the engine dosent struggle to pull it. I expect worse economy when loaded, but it shouldn't be that bad. Thanks for your replys.

 

dont throw a fag end out the window when in traffic jams. it sounds like youve got a big hole in your tank.
my 58 plate 115 350 has terrible fuel economy . £103 to fill the tank and only about 370 miles from it and it has a limiter fitted at 62mph. my 60 plate 313 sprinter got better mileage , took a tenner less to fill and it was often cruising along at 90ish.

 

If I take everything out the back, it goes back up to 30,s!!!