Are you sure the apple marks are bruises? They could perhaps be caused by lack of calcium, I think it is. Ah yes, from Chris Bowers:
<< Bitter Pit
This is a physiological disorder caused by a lack of calcium in the soil. Calcium can be given as a supplement but often the problem arises because of the trees’ inability to take up and absorb the calcium. For this reason heavy watering during dry spells can help, as will a good mulch. Often cookers seem worse affected than eaters, but many varieties can be affected. Fruits may appear ‘good’ on the outside but when cut the flesh is riddled with small brown speckles and spots and may have a characteristic bitter taste.>>
At least you have some plums. We had plenty of blossom but not a single plum, golden gage or damson. Very few apples on most trees except my 'I've forgotten its name' cooker and my Blenheim Orange eater. The cooker has a good crop of so far blemish free fruit, and the BO has a handful of fruit.
Have you had drought conditions this year? We have had the worst drought of the 26 years we have lived here, with many young trees losing their leaves back in June, so perhaps your problems are related to that?