I got this recipe from a the Sainsbury's magazine. It tastes divine - so summery and the colour is perfect pink. it makes about 500ml.
200g caster sugar
Juice of 3-4 and finely pared peel of 2 unwaxed lemons ( about 175ml juice)
2 tbsp sifted icing sugar
Puter the caster sugar in a pan with 200ml water and the lemon peel. Stir over a low heat until the sugar has dissolved, then bring to the boil and boil vigourously for 2 minutes without stirring. Set aside to cool. Mix in the lemon jjuice and strain in to a large bottle or jug. Whiz the raspberries with the icing sugar in a blender and strain in to the lemon mixture, discarding the seeds. Stir together and chill. To serve, dilute to taste with chilled still or sparkling water.