from all the thrashing out on this and other forums I think it can be concluded that these later 148BHP engines are more "euro compliant" and therfore have been designed by mercedes to give lower CO 2 emissions rather than economy and performance, my 2001 C220 CDI (manual 6 speed) never dropped below 40MPG and was quicker with only 143BHP.
I love the car, and I guess I just have to get used to the fact that £70 worth of juice does about 450 miles.
Its questionable wether the CDI model is worth buying over petrol Kompressor... I had a 56 plated auto on hire (C180k) that constantly gave 35MPG....and a much more pleasant drive.
Sigh