I hate to admit it but the cruise control can drive more economically than me ! I've tested it several times and I admit it.
I live in rural Norfolk with mainly flat roads and get 28-30 mpg with my 2 litre auto. I have had more on a long run driving at around 60 mph on A roads (A47, A17 and A1). The car has 50k miles on it and I drive like an old grandad (because I am an old grandad!).