These are typical photos of wrinkly leaves, that in this instance are on blackcurrant bushes. But the same effect can be seen on many species, be it cherries, apples or plums etc. In nearly all instances its due to aphids. These are many varieties of aphids, but these are probably Currant-sowthistle aphids (Hyperomyzus lactucae).
Aphids will damage shoots and reduce fruiting, as well as spreading plant viruses. So get rid of them, or let the ladybirds at them. They start building up during spring. But come June they start spreading to other plants. When winter comes they over winter as eggs under the bark.