Is it a dwarf variety or is it a large pot? Apple trees use lots of water and you do need to feed them with bonemeal or the like to encourage fruiting buds. Do you prune the tree? Am wondering if you are cutting off the fruit buds and leaving the leaf buds?

I have two in pots and they were new last year. It is recommended that you have an apple tree within 30 metres of yours to pollinate. Both of mine produced fruit last year.

Does it come into blossom? Is it in an exposed position where the blossom is burnt off by early season frosts? Polinating bees will fly many hundreds of yards to collect nectar and even if the tree wasn't self-fertile I would expect some sort of fruit. As already said the tree needs lots of water so I would take it out of the pot with as much of the surrounding soil as possible and plant it in the garden in a sunny position. A fruiting tree that is put under stress will drop any emerging fruit and then the leaves. On further investigation, as you are far north then the weather might have something to do with it. There is possibly some varieties of apple which will thrive so far north and an internet search might help.