Tip the sugar and 1 litre water into a saucepan over a medium heat and heat, stirring, until the sugar has dissolved. Remove from the heat and leave to cool completely.

Put the strawberries in a blender and blitz to a purée. You can strain this through a fine mesh sieve to remove any seeds, if you prefer. Tip the strawberry purée into a large jug with the sugar water and lemon juice, and stir to combine. Pour into glasses filled with ice and serve garnished with whole strawberries, if you like. Will keep chilled for a day.