Strip the redcurrants from the stalks using the prongs of a fork. Hull the raspberries and combine the fruits. Place in the base of a 1-litre (2-pint) baking or pie dish. Sprinkle with the sugar and add the water. Set aside while preparing the crumble topping.
Sift the flour into a mixing basin, add the butter cut into pieces and rub into the flour. Add the sugar and continue rubbing in