UPDATE..
Left work last night,with a 17 mile trip home and 25 miles too go showing, and no fuel light on, hit 20 miles left in tank, and fuel light came on, filled up with 5 miles to go showing, tank took 51.28 ltrs to brim it, or 11.29 gallons,the trip showing 315 miles, so MPG 27.9
I find that a bit pointless, when a car that does around 27 MPG has a fuel low light that comes on so late.later in fact then my GTi which came on at 45 miles to go, and did 33 MPG.