I've been charging with the granny lead on a fused outdoor extension, plugged into the kitchen socket circuit (dedicated) overnight, after our dinner-making usage has stopped.
Our wiring is 2 years old, has 100a breaker, and I turn the charger off if we use the kettle. Everything else on that circuit is off. There has been no heat in the extension or the plugs. The kitchen has a smoke detector. The smart meter is showing 2kwh pull from the charger, the car is showing 1.87kwh charging at the car.
It's costing around £20 for 200 miles usage for the week. Off peak at 10p/kWh it would cost less than £7.
This is only a temporary measure until we get the OHME installed. In which case I'll switch over to Intelligent Octopus tariff, and charge with the 7kw charger in the 6 hours off peak.
My day rate will increase by 20%, but we are fairly low home users, and can timeshift the washing machine to off-peak to save on that.