The Green Vehicle Guide on the windscreen of my 2012 Opel Corsa said the car’s combined fuel consumption is 6.3 L/100 km. After 21,000 km my average is 7.9-8.1 L/100 km. The combined consumption of the Nissan Micra I traded on the Corsa was 6.4 L/100 km. I ran it for 40,000 km and it was virtually spot-on. The Corsa is a 1.4-litre, the Micra was 1.5-litre. I drive the same way and I drive in the same areas with both cars. When I questioned the dealer they took it for a 28 km run and said there is nothing wrong with the consumption. They also suggested I contact the Green Vehicle Guide, which I did, and they told me the fuel consumption was high because of the way I drive.
The combined fuel consumption quoted on the label on your windscreen is not a real-life figure, it’s the result of a laboratory test, and the aim of it its to provide the buyer with a figure they can use to compare one car with another. The bottom line is that it doesn’t necessarily affect the consumption you might get in real life driving. But I would expect the real life fuel consumption to be closer to the claimed figure than yours appears to be. There are many factors that can affect fuel consumption, ranging from tyre pressures, extra load in the boot, roof racks, driving style etc. I would ask the dealer to demonstrate to you that the car’s fuel consumption is normal, as they claim it is.