Graham
I am amazed at your patience - you should have currants from year
three.
Do you know what variety it was you planted?
Can we go over growing a blackcurrant - forgive me if you have been
there and done that - but at least know that you have knocked off the
items on the list.
Blackcurrants, unlike redcurrants, are hungry nitrogen feeders. FYM
is typically applied as a mulch in February. If not available then
bone meal / pelleted chicken manure can be used to supplement garden
compost. Soil wise they are not fussy (except chalk soils) so long as
they are fed. Can be grown on chlk if a large planting hole is dug
and good soil put in.

Blackcurrants are grown as a stool bush, the plant is planted lower
than it was in the pot / nursery. The ground it goes in wants to be
fertile and enriched. When the first rooted curtring is planted it
should be cut back to three buds above the ground so that it thows up
new wood from below the ground. This is where most people go wrong
on buying a new plant, they fail to cut it back. The aim is to
eastblish 5-8 main branches to start the plant off.
The following year reduce the new growth by half. No further pruning
will be required for two years as a well fed bush will produce pleanty
of new growth. The fruit appears on last years young wood, whereas
your redcurrants fruit on old wood. Here lies the difference in the
culture of the two plants. Redcurrants are pruned like gooeseberries
- to encourage the formation of fruiting spurs, whereas pruning
blackcurrants is about renewal pruing - that being the removal of one
third old wood at the point of origin. OK cutting out old wood takes
away young wood - therefore fruit. But if there is more old wood than
new on the branch, then it is a candidate for removal.
You can get fruit in year two after planting a cutting - but doing so
leads to spindly growth. The wood produced it much more dense /
thicker than redcurrants, it does not want to be spindly.
The commercial life expectancy of a currant bush is 8-12 years, though
the gardener may eeek out longer.
Space - most blackcurrants are vigourous growers - a bush of 6ft
spread is typical.
They grow well in the UK and there are commercial growers down in the
south of England up into Scotland - growing for juice. yes 98% of all
UK blackcurrants go into ribena (and all grown under environmental
stewardship shemes). The flowers are frost sensitive. Again
commercially they have a technique used but French grape growers who
spray the plants with water - to encase the plant in ice to protect
the flower from the rapid thaw of frost, the ice thaw is gentle and
insulates the flower from the cold - apparently. Attended a talk
given by an ex Beechams man (owner of Ribena) whio had some great
slides of fields of icicle laden blackcurrant bushes.
Revertion and big bud disease are the main issues with blackcurants.
Removal and burn is the only corrective measure. Do not propogate from
them. If you are unware of what big bud is - it is a disease caused
by a mite which attacks the buds which are enlarged. In reversion the
leaves of an infected plant have desribed as being nettle like in that
they have three elongate lobes and there are three rather than five
main veins in the leaf.. The old winter tar oil wash was a good
control of the mite but alas no longer available.

If the plant is healthy and not suffering from reversion or big bud
then my gut feeling is frost damage to the flowers

Good luck
Clifford
Bawtry, Doncaster, South Yorkshire