Just after we set off today the fuel warning came on - 35 miles remaining.
On the Mk6 GTD it would come on with 50 miles remaining. I learned that the car would do another 30 if driven sensibly. Our A3 does something similar.
So anyway, I was not really worrying. I worked out that the car would read 0 miles just before I reached the Sainsbury's petrol station. On arrival, I noted the mileage and filled the car to the neck with Super Unleaded. When I looked at the pump it said 53.71L

I was aware that the old MK6 had a 55L tank, but our A3 has a 50L tank. I checked the Golf brochure in case they changed tank size on the Mk7.5. It says the GTI Performance has a 50L tank.

I see 3 possibilities -
1. I was driving on fumes. This means the fuel gauge is completely accurate.

2. The pump was wrong.

3. The tank is bigger than 50L.

I'm guessing I was driving on fumes?

Just in case anyone is interested: the mileage was 403, I calculate that to be 34mpg.