Melt the margarine with the sugar and honey.
Mix together the porridge oats and muesli, then pour over the melted margarine. Mix very thoroughly and spread into a 7"x 7" greased baking sheet.
Bake at 190 C/375 F/gas mark 5 for 20-25 minutes or until golden brown.
Remove from the oven and mark into triangles, leave to cool completely.