I've tried various methods to deter bullfinches from devouring the newly emerging buds of apple blossoms, full of promise and, obviously, delectable sweetness. Forget about old CD-ROMs, streamers made out of baler twine and cut up old fertiliser bags (but see below), and feeding stations with alternative seed and breadcrumb offerings (although this works for a neighbour of mine who's only got a few apple trees and puts a platform in each of them). Neither did I spray the trees repeatedly with some bitter herbal concoction – this would have been my absolute last resort even though I lost almost all my crop for two consecutive years in a few days of bullfinch feeding frenzy.
What is needed is something that's big, unnatural looking, rustles noisily in the slightest breeze and (unlike the bitter spray presumably) doesn't require renewal after every shower – in short, old plastic bags! They do look rather unsightly, no doubt about it, but they are only necessary for a few weeks (you can improve their appearance and effectiveness somewhat by liberal application of above mentioned streamers or similar) and, boy, do they work! For my largest tree I used a whole fertiliser bag, hung up in such a way that it could turn freely and easily.
If your currants and gooseberries are gobbled up by blackbirds and you don't fancy netting them (maybe it's impractical for some reason), pick them a day or two just before the birds would, and leave them to ripen in large bowls. This way you can control the amount you and the birds get – they deserve some too!
I'm looking forward to this year's crop!