Make the nut brittle. Place the sugar and measurement water in a saucepan and cook over a low heat until the sugar has dissolved, then increase the heat and continue to cook until the mixture is a golden caramel colour. Place the nuts close together on a baking sheet lined with baking paper. Pour over the caramel, then leave to cool until completely set and hard. Smash up the nuts with a rolling pin and then, reserving a few big pieces for decoration, place the remainder in a food processor and pulse until mostly broken up.
Whisk the egg whites in a clean bowl until stiff peaks form. Gradually whisk in the sugar, a spoonful at a time, until stiff and glossy. In a separate bowl, whip the cream until it just holds its shape. Gently fold the meringue into the cream in 3 batches. Stir in the honey and pulsed nuts. Spoon the mixture into a 1.2 litre (2 pint) loaf tin lined with clingfilm and smooth the top. Place in the freezer overnight until firm.
Transfer the parfait to the refrigerator and leave to soften for 10 minutes. Turn out on to a plate, scatter over the reserved nut brittle and serve cut into slices.