fuschias leaf drop

Are you sure they aren't getting too hot? Maybe they would be better outside in warm weather.

There is a possability that they may have been attacked by Vine Weevil. They are small white grubs which chew the roots of fuschias and primulas, causing them to have leaf drop and eventually killing the plant. I have revived plants by first taking them out of their pots and brushing off the compost and removing the offending beasts and repotting in fresh compost. Vine Weevil treatments can be obtained from garden centres.