Combine the gin and lemon juice in a cocktail shaker with a handful of ice. Shake for 30 seconds, then strain into an ice filled glass. Pour the blackberry syrup over the top and stir.

In a medium sauce pan, combine the water and sugar on low heat until the sugar is melted.

Lightly muddle the blackberries in a long, shallow tub. Then pour the syrup over and let it sit for a few hours. Strain to remove the blackberries, then bottle the syrup and place in the fridge. The syrup is good for a week.