Filled the car up fully a week ago, and Im already down to less than half a tank, I haven't made any extra journeys so a bit worried, also there's no puddles around the car or if its been sat, theres nothing when I leave. It did this last time I filled it up to the top, the first half disappeared fast, then the second half slowed down and lasted another 2-3 weeks as I only use the car to go to work and back.
This could be an issue with the fuel gauge sending unit. I have a vehicle with the gas gauge that stays near "full" forever, then drops very quickly from "half" to "empty". The sending unit simply isn't linear.
Watch the number of gallons of gas you buy and the mileage you drive, then calculate your fuel mileage. If it's normal, suspect the sending unit, not the engine.