And the good news is that a fully charged 12V battery cleared the problem.
I agree that opening the door with a flat battery shouldn’t be an issue as there is a key blade inside the fob. There isn’t anywhere inside the car to fit the physical key but you can at least pop the bonnet and charge the car.
Loads of error and visit dealer signs were cleared by turning in off and turning it on again several times, also driving it backwards and then forwards a few feet.
Normal service now resumed but basically a flat 12V battery in an EV is more of a pain in the arse than in an ICE car.
The good news is that the car issues provoked a debate with the wife that has possibly ended with me getting to go ahead for a Bentley GTC 6.0 W12 which compliments the Leaf nicely I think.