Peel and core all the apples and cut them into walnut-sized pieces. Place them in a bowl with all the remaining ingredients except the filo pastry and butter. Toss gently together and leave on one side.
Preheat the oven to 190 degrees. Unroll the filo pastry and check that all sheets are unbroken. Cover with a cloth to prevent them from drying. Brush a baking sheet with a little of the butter.
Lay a clean tea towel short side towards you on the work surface and lay a sheet of pastry on top, long side towards you. Brush with a little butter and place the next sheet on top of half the first sheet, increasing the depth.
Brush again with butter.
Place the third sheet over the area covered by the first sheet and continue layering and buttering as before. Using a slotted spoon, pile the fruit along the length of the front edge making sure that the prunes are evenly distributed.
Lift the front edge of the tea towel up gently, and carefully but firmly begin to roll the pastry around the apple into a sausage shape, tucking in the ends to prevent the apple from falling out.
Just before reaching the far end, brush the final 2cm of filo pastry with butter and press the roll over this to seal it well. With the aid of the tea towel lift the strudel on to the baking sheet and bake for approximately 30 minutes or until crisp and golden. Serve warm or chilled the following day with lot of whipped cream.