Line a 450g loaf tin with a double layer of cling film.
Boil blueberries, currants, sugar, and water in a pan for 3 minutes until softened.
Stir the raspberries and blackberries into the hot fruit mixture without further cooking.
Remove crusts from the bread and cut into long, medium-thick slices.
Line the base and sides of the tin with bread slices trimmed to fit.
Spoon enough fruit and juice into the tin to thoroughly soak the bread.
Fill the tin with half the fruit and seal the top with a final bread slice.
Cover with cling film, add a weight on top, and refrigerate overnight.
Invert the pudding onto a plate, slice, and serve with remaining berries.