Thank you both.
It's good to know that it isn't "unusual".
Temperature here today is a fairly warm 19'C - and it fluctuated during that.
However, we did 11 miles this evening with the range starting on 23 miles - and it finished up with 10 miles left, so not too bad - we lost two but to be fair, we did put the aircon on for about 3 or 4 minutes.
We are enjoying the car a lot. I'm very impressed with it and it is nice to drive. I've watched a lot of videos on line and read quite a lot of this forum before we even bought it (research!) but I know we still have a lot to learn about it. Understanding how it reports stuff is probably the hardest. Also, I noticed in the handbook that the explanation of Eco Mode is pretty minimal, so most times we are driving with it in Normal mode.
When I bought the car, I had a 185 mile journey home, most of it by motorway, so I drove up to the motorway in normal mode, then switched to Battery Save whilst travelling at speed, then back to Normal once off the motorway. I managed to get 47.3 mpg.
Currently, with mostly local driving, the display is just showing --.-, which I have read means it is over 100mpg. Is this something that is per trip or is it an average?
Anyhow, thanks for the welcome and the advice.