I'm on the Orkney Islands.
We don't have varroa (yet), but our honey harvests are very limited due to long winters and low summer temperatures which are rarely above 20 degrees C.
Spring buildup on willow and flowering currant, then dandelion and sycamore.
Usually, white clover is the only crop that we harvest, but some of us are lucky and get some heather honey.
Harvests per colony vary a lot with locations, I think the most I have heard of was about 50 kg per year.
I don't recommend anybody should keep bees here commercially, but it's still a great hobby.