The coating of powdery white fungal spores tends to appear under humid conditions at this time of the year, and is particularly seen when the plants are dry at their roots.To treat it, spray the plants with a systemic fungicide on a dry, overcast day. There are lots of fungicides available in garden centres. You can spray them but there will be a delay of several weeks before it is safe to harvest and eat any fruit. You will need to check the manufacturers instructions for the recommended safety measures.
If you are thinking of replacing your gooseberries then try to go for a mildew resistant variety such as Invicta http://www.thompson-morgan.com/fruit1/product/cww3195/1.html or Xenia.http://www.thompson-morgan.com/fruit1/product/cww3551/1.html