>>>How is the best way to get bananas (musa, various species) to fruit in
UK? without being in a greenhouse?<<<<
Bananas bear alternate years. They need about 18 months of temperatures of
steady temperature of about 75-82 degrees (with 40 degrees minimum) to
really thrive. They also require protection from wind to keep the leaves
from tattering badly. And full sun, probably 10-14 hours a day. They do
best in rich mucky wet soil. Those growing along a lake shore or over a
septic tank do the best. The more organics and nitrogen the better for the
first year. After bearing the top dies off and the plant resprouts from the
corms, and can be divided at that time.
In UK I would suspect that you would really need a heated glassed enclosure
and supplemental lighting of some sort to get them to set. If they get too
cold or dry they simply stop growing and won't set fruit.
Dwarf Cavendish variety is one of the most cold tolerant, and tops out at
under 10 feet, small enough for a small enclosure or interior sun room.
Also Musa coccinea would be worth trying.