Pear & rosemary syrup
Bring the water to the boil along with all the other ingredients up to and including the rosemary, stirring constantly, reduce over a medium heat for approx. 25 mins. Pour the syrup through a sieve (yields approx. 400 ml). Don't squeeze out the pears, otherwise the syrup will become cloudy. While still boiling hot, pour the syrup into a clean, warm bottle and fill to just below the rim, seal immediately, leave to cool.
Gin and tonic
Place 6 tbsp of syrup in a shaker along with the ice and gin, shake well. Place the ice cubes, pear and rosemary in the glasses, pour the gin through a sieve and add it along with the tonic water.