Cut the tops off the lemons and carefully scoop out the flesh.
Cut a small slice off the base of each so they stand up, taking care not to make a hole in the base.
Place in the freezer.
Puree the flesh in a blender or food processor, then strain into a bowl.
Heat the sugar, water and glucose in a saucepan until the sugar has dissolved.
Bring to the boil and boil for 1 minute.
Leave to cool.
Stir into the strained lemon juice and add the gin.
Pour into a shallow container and freeze for 2 hours until hardening around the edges.
Whisk until all the ice crystals have broken up.
Return to the freezer.
Whisk again after 1 hour, then freeze until just firm.
Pack into the lemons and return to the freezer.
Transport in a cool box surrounded with ice packs.