Preheat the oven to 180C.
Mix the flour, sugar and baking powder together in a bowl with the grapes and blueberries.
In a separate bowl lightly beat together the egg, yoghurt and oil.
Fold the wet mixture into the dry mix until it's well combined.
Fill a muffin tray and place it in the oven.
Bake for 25 minutes.
Remove from the oven and set aside to cool slightly.
These also freeze very well, so pack some aside and enjoy them again later on in the month.