Magna E10 consumption

I own a 2003 TJ Mitsubishi Magna that has averaged about 12-12.5 L/ 100 km around town using regular unleaded, but when I have used E10 the fuel consumption has blown out to 17.5-18 L/100 km and it ran a little rougher at idle. When I reverted to regular unleaded the engine ran smoother again and the fuel consumption returned to what it was before. Based on those fuel figures, my car uses about 40 per cent more fuel on E10, not the one to three per cent more you write in your recent story. I can't help but wonder if the government is giving us a bum steer.