Your figures sound fair to be honest.

Stop start London traffic is going to drink fuel, and any speed over 60mph unless the car is extremely sleek you are shifting lots of air and the volume of air you shift increases dramatically above 65 or so, our C2 VTS 16HDi would drop from near enough 60mpg at 60 to below 40 at 80mph.

Tyre pressures set at the high speed pressures?, tyres themselves a decent brand and type?

We can all improve our driving, simple way is to imagine you only have the parking brake so you keep your distance lifting off the throttle a long way from junctions and try to time your junctions so you have to brake only minimally and never actually come to a halt, maintaining smooth progress is always more economical.

One thing you could check is that the brakes are not binding, on a dual carriageway drive without braking for several miles at a steady speed then when you see a layby on an uphil section lift off early and, using the hill and manual gears for slowing stop in the layby without touching the brakes at all, then get out and feel carefully round the wheels hubs and discs/drums for heat, there will be warmth through road friction but the discs and drums (possibly drum inside disc rear parking brake on this model but only guessing) should be cool all round.

Edited by gordonbennet on 23/07/2017 at 18:03

Have you checked that your brakes aren't binding? At the end of a journey feel the wheels to see if one is warmer than the others. I had a dragging caliper on my car and it was easy to spot being a manual -the car just didn't freewheel with the clutch down as easily as usual. Maybe you wouldn't notice with a CVT.

It's a possibility that it's been driven very gently before you bought it, and there are deposits building up in the engine. Maybe a good thrash (when warm) or running some injector cleaner through may help if so.

EDIT - gb beat me to it!

Edited by corax on 23/07/2017 at 18:09