Hi,
Samwell your absolutely right,i filled my car up today for the first time when the fuel light came on,it only took 40 litres to fill it,so with the reserve holding 5 litres plus the additional 40 litres i added this obviously equals a 45 litre fuel tank,this goes along way to explaining why i'll only achieve between 250-300 miles on a full tank.
I know the handbook suggests the fuel tank should hold approx 55 litres but i can assure everyone mine only holds 45 litres.