Probably the fungal disease called scab causing the
brownish/black spots and some yellowing/dropping of the most
damaged leaves. Spores are dispersed on the wind and land on the
leaves. When the leaf surface is wet for several hours
(including water droplets which remain for a few hours after
rain stops), the spore can germinate and infect the leaf or the
fruit. Some years and some varieties suffer worse than others.
There is no cure once infected, but the problem may not occur
next year depending on the weather. Some varieties have
resistance to scab; especially the really rare varieties. The
common varieties tend to be very prone to scab. The leaves
looking like they've been attacked is nothing to worry about,
unless your tree is a dwarf and therefore unable to care for
itself, Big trees don't need help. In fact, birds are often
attracted to plants with tatty leaves in the hope that they can
find an easy meal (a caterpillar). Lack of fruit could be cold
weather affecting bees (therefore no pollination). Som