I have figured out how to get the car to tell me fuel efficiency on each trip. It's a Renault Scenic 1.6. Manufacturer says 38 mpg, I am getting 39-40 mpg in city and up to 42.9 mpg on motorway / A road.
How? Well I don't go above 65 mph if I can help it, and generally stay around 60. Once upon a time I would generally cruise, well let's say a little (but not too much) above 70! But that's when petrol was 60 pence per litre and I had a Cavalier and then a Laguna which were more designed for motorway slogging.
Now with petrol at 133 pence per litre it makes sense on a lot of levels, not just from a petrol saving point of view to slow down - less emissions for a start, it's safer as well. And it doesn't really add too much to a journey time.
Also the way I drive has changed, smoother acceleration/deceleration when possible, trying to cruise at an even speed, using the gears efficiently and so on.