Feed every 6 weeks during the growing season. I use
Ericaceous liquid plant food, so do the Raspberries the
same time as the other Ericaceous plants.
Check growing instructions for Blackcurrants re fruiting
on new growth.

Blackcurrants are hungry. Try a thick mulch of well rotted manure over the winter and some sulphate of potash around February, at the same time you'd do gooseberries.I guess you could use some Growmore as well for good measure but never tried it.