A thread on the Fruit and Orchards Forum is veering into Harvest Territory so I thought I'd link you up. Hope that's OK.
Here is a link that might be useful: Sugar Content
That is why Pomonas Universal pectin is so great. You can use no sugar, less sugar, whatever you want.
Don't know if they sell Pomona Pectin in the UK (did not do so in the past even though sold in North America) but I believe it is made in Denmark from Spanish citrus peels.
Maybe it is sold in the UK by now.
Jim in So Calif