Quick update,
Filled up with 250 miles on the clock today and worked it out at 22mpg overall. Currently showing 25 on the trip info, but I reset that about 80 miles ago.
Had much more use of battery power driving today as it was warmer when I left work at lunch, so I'm convinced this is a major factor. In fact, i took my mum shopping and drove the 2 miles from her house to the supermarket completely without ICE.
I'm not actually that bothered about the mpg, but I'm interested in the technology, and, of course, the health of the car I've just bought.
I'm thinking some old fashioned ideas, like covering half the rad, may help at this time of year.