Peel, core and quarter the apples and pears. Slice the quarters and add the slices to a 1.2 litre (2 pint) pie dish. Add the plums and the measurement water, then sprinkle with 25 g (1 oz) of the sugar. Cover the dish with foil and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 10 minutes.
Put the remaining sugar in a bowl with the flour, add the butter and rub in with your fingertips or an electric mixer until the mixture resembles fine breadcrumbs. Stir in the coconut and chocolate chips.
Remove the foil from the fruit and spoon the crumble over the top. Bake for 20–25 minutes until the crumble topping is golden brown and the fruit is tender. Serve warm with custard or cream.