Place a third of the strawberries in a food processor with the icing sugar and blend to make a purée. You may have to do this in batches.
Chop the remaining fruit and place in a large bowl, sprinkle over the caster sugar and set aside.
Whip the lactosee free cream in a very large bowl until soft peaks have formed then stir in the lactose free yogurt, chopped strawberries and the purée. Spoon into large bowls and refrigerate until ready to serve.