For the last 2 years the fruit on my redcurrant bushes has not turned red.
Maybe you have a white currant? Did you taste them?
Love whitecurrants http://www.crocus.co.uk/plants/_/whitecurrant-versailles-blanche/classid.2000017965/
When mine don't ripen, it's because the blackbirds pick each one off the stalk before I get to see it. So, if your bunches of green currants get smaller and still none ripen...
The bushes are cuttings from a very old variety and the berries look like white currents but just don't turn red as in previous years.