Combine the berries, sugar and water in a medium pan.
Stir gently over a low heat without boiling, until the sugar has dissolved.
Simmer without stirring until the juices are released from the fruit, about 5 minutes.
Strain the juices from the fruit in a sieve and reserve.
Lightly butter a 3-4 litre glass bowl, sprinkle with a little caster sugar and shake away the excess.
Cut half the bread slices into triangles, leaving the rest in squares.
Line the sugared bowl with the triangular bread slices around the bottom, firmly packed to totally cover the base.
Line the sides of the bowl with the squares of bread, overlapping slightly.
Fill the strained fruit into the centre of the bowl and pour enough juice in to nearly cover the fruit, ensuring the juices run though the bread slices lining the bowl, to colour.
Cover the top of the fruit with more triangular pieces of bread, overlapping and pour a little more juice over to saturate the bread.
Place the bowl in a larger dish so as not to spill any juice and weight the pudding down with a flat plate that fits perfectly on top.
Refrigerate overnight to allow the pudding to set.
To serve, remove the pudding from the mould, slice and serve with double cream.