Manufacturer's handbooks always recommend a period of bedding in, thus ensuring the longevity of the engine placed in your chosen purchase.
Despite the figure you've posted, provided that you're not red-lining your Up! on the motorway, I'd certainly expect that figure to improve as the engine beds in.
I currently attain between 55-60mpg in my 75 bhp High Up! which is largely used around town and upon Motorways roads, where my speed can be anywhere between 0 - 70 mph.
Hope this helps.