Colin Hammond writes
For some years a large established eating apple tree in my garden has
stopped fruiting. I suspect is not self fertile and it stopped fruiting when
a neighbour cut down their tree. I've no idea what type of tree I have. Any
rule for picking a pollinator in this situation?

Wait till it flowers next spring, find a nursery or garden centre near
you with same sort of growing conditions that sells apple trees, choose
one that is in flower at the same time.
--
Kay