Mix the strawberries, raspberries, sugar, lime zest, lime juice and sage in a wide pan, bring to the boil, then boil fast for approx. 4 mins. while stirring. Puree the mixture, return to the boil. 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.