To make the juniper syrup, put the sugar in a saucepan and add the measured water. Heat over a low heat, stirring occasionally, until the sugar has completely dissolved.
Add the juniper berries and citrus rinds and bring up to just below boiling point, then simmer for 10 minutes. Take off the heat and leave to cool.
Strain the syrup through a fine sieve into a wide-necked jug or bowl. Pour through a funnel into a sterilized bottle or jar, seal and store in the refrigerator for up to 2 weeks.
To make the NG&T, add the ice to a large glass, followed by the slices of orange and lemon and juniper berries, then pour in the juniper syrup. Top up with tonic water and serve.
Tip: You can buy juniper-flavoured spirit substitutes online instead of making juniper syrup, if you prefer.