Yes, assumes E7 and charging at night. In practice I charge more than 50% at work, and "some" at Superchargers, so my rate is probably better than that.
If you are coming from a Super-Eco car then the savings won't be that good, I'm starting from a similar sized car as a basis.
Assuming 30 MPG for existing car then:
Petrol = 4.54 (Litres) * £1.20 / 30 = cost per mile = 18p / mile
Assuming 3 miles per kWh and £0.08 per unit for E7:
£0.08 price per kWh / 3 = 2.5p / mile
10,000 miles saving = 10000 * (0.18 - 0.025) = £130 per month - if you don't have E7 (well ... get it fitted!), or your comparison-car is better than 30MPG you'll be nearer £100 per month