On the end of the wiper stalk there's a clicky to cycle through info about mileage, fuel consumption etc. There should be an average mpg option which although you need to take with a pinch of salt (and you need to give it a long drive to get a true figure), should give you an idea of fuel consumption.
In city driving in my 2006 1.4 75bhp I average about 33-37mpg. Out on the motorway this climbs to 40-43mpg, and on a 60mph steady A-road I can hit 46-53mpg if I'm feather light on the throttle and there's not too many hills. That's using standard cheap fuel.
I did get poor MPG recently and it was down to two things; I needed a new air filter, and my handbrake was slightly too tight and was binding. Easy enough to loosen up, plus if your rear drums are unusually hot after a drive it's a sure sign.
A lambda on its way out may cause the
problem but I'd expect to see an engine light by that point, personally. I actually swapped out a faulty lambda recently and my average MPG went DOWN a little bit, although I do feel the car more responsive.
Driving style does contribute a lot too in these little cars as they need to be revved hard to get any power out of them. Saying that, I can do a B-road blast in mostly 2nd-4th gear and still average out at about 37mpg which isn't too bad.
