I decided as the weather was a beautiful 16C today to bite the bullet and split the double brood box hive. I may regret this but as the colony size was massive I was concerned they would suddenly swarm if I missed just one of the queen cells in the next week or so.
After checking both brood chambers had eggs and larvae I removed the top brood chamber and placed it onto a new floor then lifted the two together and set them up a stand 15ft away. As most of the flyers will return to their original site I gave the upper half the super which is about 3/4's full of mostly crystallized honey. It doesn't matter which half have the queen but I will check them both again in a week or so to see which has built queen cells then leave that one alone for the next few weeks to let them bring on a new queen.
These bees are very defensive compared to the carni's I have, these girls go all out to sting as soon as they land. Thankfully a small amount of smoke and they will fly off again with their stingers intact.