brian mitchell writes

But maybe I asked the wrong question. I have some Whinham's Industry
gooseberries which are supposed to be a dessert variety and they seem
ripe --dark red all round and coming away easily-- but very tart this
year so I wonder if the lack of sun equates to less natural sugar?

Perhaps. Though mine are Whinham's and I don't find them in the least
bit tart when picked red. Mine are growing under a mock orange, so
perhaps it's not sun so much as warmth.
--
Kay