Place the gooseberries and elderflower syrup in a pan, cover and simmer for approx. 10 mins. Add the sugar, bring to the boil over a medium heat while stirring. Boil fast for approx. 10 mins. Ladle the jam into the clean, pre-warmed jars while still boiling hot, fill the jars to just below the rim, seal immediately. Briefly upend the screw-top jars, leave to cool on an insulating surface.