Butter a 1.2 litres/2 pint heatproof bowl and dust with flour. Preheat the oven to 180C/350F/Gas 4.
In a bowl, mix the flours, sugar, baking powder and cinnamon together. In a separate bowl or jug, beat together the oil, milk and eggs. Pour this onto the dry ingredients and stir to combine. Fold in the apple and toffee pieces.
Pour into the prepared dish and bake for 50-60 minutes. Test the cake is cooked through by inserting a skewer into the centre, if it is cooked it will come out clean.
Leave in the dish to cool for 10 minutes then turn the cake out. Leave to cool completely and serve.