Place the sugar and lime juice into a highball glass and stir until dissolved.
Wipe the mint leaves around the rim of the glass, then tear them in two and drop them into the glass.
Crush the mint leaves lightly with the back of a teaspoon.
Fill the glass with crushed ice.
Add the gin and chilled green tea and stir well.
To serve, garnish the glass with a sprig of mint.
