On recommendation bought a Energenie ENER007 Appliance Power Meter.
Car arrived home with Nil electic mileage range, (petrol engine running for last 10 minutes to get home), so happy battery "empty" as makes no realistic difference.
Charge amount shown this AM as 17.16Kw. My electric cost 32/p Kw = £ 5.32 for 40 "range miles"*
* what the car now claims is the current electric only range.
Current Petrol 95Ron** @ £ 1.48/litre = £ 6.72/gallon
** Don't know what 98Ron costs
So there you have it, you save £ 1.26/gallon, and on 12,000 mile a year that 300 Gallons @ 40MPG saves you ....less than £400/yr, or £ 1134 over 3 yrs
Else where I have a thread about MPG with only petrol engine in "save" and "charge" modes, and I get approx 40MPG @ 60mph on A1M type roads.
Shame the car cost me >£5k more to buy than a non- hybrid..
Cheers
Bob