So I am deciding to stick with momentum. Filled up the tank today after doing 255miles of mixed driving, mainly town driving, cold engine, a few blast here and there on motorway and A/B roads. It took 56.33 litres = 12.39 gallons.
This amounted to 20.55mpg. Trip computer said I was averaging 25.7mpg (a bit optimistic). In all, I am quite pleased with it. At this rate, it could well do 300miles on long motorway cruise ^_^