There are now a number of varieties that are resistant to American
Gooseberry Mildew
Hamamakki Red, Yellow and Gold
Hino Red
Invicta
Pax
Greenfinch
Jubilee (also known as Careless Jubilee - telling a little of its
parentage)
are but a few
www.agroforestry.co.uk lists a number of these

If you want to stay with traditional fruit that does get it, pruning
to encourage air movement is one important task, but also consider why
it occurs. The mildew typically happens when the air around the plant
is damp, so avoid damp shady locations, keep the ground beneath the
bush clear of weeds and other plants (turf or meadow plants) and train
the bush so that the branches do not weep downwards and restrict
growth (something that Invicta does). Also don't plant too close
together. THe fungus sheds its spores in the autumn so good hygiene
beneath the bush is important, removing any mulch (which will also
help limit over wintering sawfly)

Treatments have been suggested but the mildew does wash off with a bit
of rubbing.

Good luck

Clifford
Bawtry, Doncaster, South Yorkshire