Welcome to the board, Northern Banana Grower.
What size polytunnels will you be using? How tall, wide, and long?
Regarding variety, your concern about food security makes me think that 'kcal of fruit per square foot of growing space' would be important, so you'll probably be looking for varieties that produce large bunches.
The Cavendish varieties are workhorses in that regard. They're the big yellow bananas you see in grocery stores.
Dwarf Cavendish will fruit around 4-6', and the ultra productive
Grand Nain (a slightly larger type of Cavendish) will fruit a foot or two taller than that. Cavendishes are pretty cold sensitive, so the winters may slow them down a lot more than some of the hardier varieties, but their bunches can be stunningly large, and their flavor is what most people are most familiar with.
Dwarf Namwah is a bit more cold hardy. Its bunches will tend to be smaller than Cavendish bunches, but they're still big. They'll probably flower around 6-7'. The fruit is petite and generally considered to be tasty.
There's a "Wiki" link in the blue bar near the top of the page that you may find really useful. I had a field day reading through all the banana descriptions there when I first joined the forum.
Glad to have you aboard
