Does any one know what this leaf problem is called, so that I can take action to get rid of it
Well, overall the tree does not look too bad. The fruits look as if they are developing normally and there are a number of leaves that don't share the same effects as the ones you highlight, and others that have the same effect but not to the same extent.
Note that the blotched areas don't show signs of starting from a point and spreading outwards, so likely not an infection of some kind. The big leaf at the top left showing some purpling may be demonstrating two effects: the single large patch at the tip and also the clustered spotting back in the main body of the leaf, two separate areas probably looking at separate causes. The tip may be just mechanical damage that results in necrosis or death of tissue due to squeezing or incomplete expansion when young, so let's set that aside for now.
The spotting is more a deficiency of some kind. You can find a number of references online with pictures of the effects of lack of specific nutrients. Note how the spotting largely avoids the leaf veins. Action at this time might be to take a soil sample and get it analyzed for suitability for growing plants. You may find that one or several components need boosting. Also top dressing the soil with a good broad spectrum compost or rotted manure might benefit the tree in the longer term.
Keep in mind that the weather can have a dramatic effect on the ability of a tree to take up nutrients. Periods of extreme dry, wet, heat or cold can produce deficiency symptoms by the effect on soil chemistry and the ability of roots to absorb what the tree needs.