Combine the water and the sugar in a saucepan and heat over a medium heat, stirring until the sugar dissolves. Once the sugar has dissolved, add the butter, vinegar, syrup and red food colouring.
Increase the heat to moderate and bring to the boil, cooking the syrup until it reached 138°C (use a sugar thermometer to measure accurately). Skewer the apples with the sticks then dip in the hot syrup, trying to coat as much of the apples as possible in the syrup.
Leave the toffee apples to cool and harden on a lighly oiled baking tray. Serve once the toffee is hard.