Average around 23mpg here as well with a mixture of London and motorways. Purely motorways, can get up to about 28mpg or perhaps more if you try hypermiling...
I seem to be about 25mpg for my avg usage which I find odd, I live 1 mile from work and my car spends half it's life on the track. I guess every other time I drive will be on motorways and with no traffic.