It's a MorganSir....they all do that!
Well I have to say, like others, that my gauge seems to be fairly accurate. When I have managed to brim the tank (though that's another story altogether

) the gauge reads full and drops gradually as you'd expect. I tend to run it between 1/4 and 3/4 full though as trying to fill the tank results in a significant drop in the mpg due the "burp" of fuel that ends up all over the rear panel... and yes I do try to fill it carefully... and yes I know "It's a Morgan Sir... they all do that!"