Long term brim to brim average over a ten year period on mine is 24 mpg. On the dash, depending on speed and conditions I have seen up to 31mpg which equated to a real 28mpg.
Mine is chipped in the ECU so gives a better figure at steady speeds in torque lock, but uses more around town. If you use the extra torque and BHP you use more fuel. They use a lot more tootling about town at 30 MPH than they do at 65 MPH. That is why i can never understand the lowering of speed limits to cut emissions. Maybe a point in manuals. It just don't work like that on automatics.