Thanks @MikeSharp01 and @DevilDamo - that helps
So just to be clear, I could go ahead with things like a new front driveway, front porch, internal alterations and so on, but not the extension itself until I have approval for Part 1. But preparation for the extension (ie. digging foundations), might be ok to start sooner?
PS. I have asked Planning to give me a call to see if they would accept and signoff the plan from our verification specialist without having to go through the formal 8-week discharge process. Do you think they would consider that or will they be very strict about this?