Do they look like this?
It's currant blister aphid katvet. See the link below for control options.
Waste of time. Especially now. How bad is it? I get about 5 to 10% of the leaves affected and I just pick them off as they appear. But that may well be a waste of time too.
I don't think that the blister aphids do much damage, other than cosmetic, to the plants. They don't seem to affect the flowers or fruit.
I get this on my redcurrants but I just leave things alone as they do no damage. This year I got nearly 30lb fruit from 2 bushes.