Hi all, UK owner here and from my experience, I can confirm that the dash always shows a higher figure than the actual mpg. This isn't just the BRZ that does this, but pretty much all cars. If you have a sat nav that shows your actual speed, you will see that you are also driving slower than the car reports.
As an example, a display from the car of 70mph is actually only 66mph.
As for fueling, a UK gallon is slightly bigger than a US gallon (something like 1 UK gallon = 1.2 US gallons) so my mpg figure is going to show slightly higher than what you can achieve in your cars.
The BRZ manufacturer's figures show that an extra urban figure of 44.1mpg is achievable and in most cases, you can never achieve what the manufacturer's figures show because the test is carried out in perfect conditions (e.g. exactly one gallon of fuel, no extra passengers or weight). In a recent 440 miles journey which I completed on one tank of fuel, the car reported a 47.3mpg return, but the actual was only 45.4 meaning that the car's figures are 4.2% out.
This is slightly disappointing, but I was very pleased I was able to beat the manufacturer's figures.
