Place the apples in a large bowl, then cover with boiling water. Dry thoroughly and twist off any stalks. Push a wooden skewer or lolly stick into the stalk end of each apple.
Lay out a sheet of baking paper and place the apples on the sheet. Place the sugar into a saucepan along with half cup of water and set over a medium heat. Cook for five minutes until the sugar dissolves, then stir in the vinegar and syrup. Test the toffee is ready by pouring a little into a bowl of cold water. It should harden instantly and, when removed, be brittle and easy to break.
Dip and twist each apple in the hot toffee until covered, let any excess drip away, then place on the baking parchment to harden. You may have to heat the toffee a little if the temperature drops and it starts to feel thick and viscous. Leave the toffee to cool before eating.