Thanks Gents.
I'm on the Coventry at the moment and will move to the grand union at Braunston at the weekend, so looking forward to experiencing double locks!
I got an EA licence as my home mooring will be in EA waters, and got a 1 month CRT licence to cover me from Mercia to the Nene, so I think (hope!) I'm covered there. I ordered a lock key for the Nene when I applied for the EA license which should arrive soon but I wasn't aware I need a different key for the middle levels, so thanks for the link to FOTRN where it tells me where to get one