Hi Mark,
You may like to have a look on the UK Flow page to see if there is some info on brood boxes:
Or we a section “how many brood boxes” based on location.
@Paras has a few Flow Hives in the UK. Not sure if the climate is the same or how many brood boxes he uses.
Just in case you are not aware of our UK National Flow Super:
https://eu.honeyflow.com/collections/all-products/products/flow-super-uk-national-pine
This will fit on top of standard UK National brood boxes in the UK. This can be handy if you want to buy brood boxes, etc locally.