Put the sugar and 150 ml (1/4 pint) water in a large heavy-based saucepan, with a sugar thermometer attached, and heat gently until dissolved. Add the remaining ingredients and bring to the boil.

Boil until the temperature reaches the soft crack stage 132°C (270°F), when a little of the syrup dropped in cold water separates into hard but not brittle threads. Brush down the sides of the pan occasionally with a pastry brush dipped in water. Do not stir.

Pour into a greased 18 cm (7 inch) square tin. Cool for 5 minutes and mark into squares with an oiled knife when almost set. When set, break the toffee into squares and wrap in waxed papers or foil. Store in an airtight container.