Yes, I realised that those comments came from Wales but (a) given that he was responding to a comment about planning permission, I suspect that he was actually referring to permissions (be they planning and/or building control permissions) for the everything to do with the lean-to (primarily construction), and (b) as far as notifiability of the electrical work is concerned, as I said, if the lean-to building does not count as 'outside', and if the OP was only going to extend existing circuits into the lean-to, then I don't see that the work would be notifiable, even in Wales, would it?Yes, but it was someone in Wales who said he thought he would have to go through Building Control. He would.
Kind Regards, John