Preheat the oven to 190℃ (170℃ fan)/375°F /gas mark 5). Line a muffin tin with 8 cases, or grease well and dust with flour.
Place the flour, sugar, baking powder, bicarbonate of soda, and cinnamon in a large bowl. Add the nuts and stir to combine. Make a well in the centre.
Beat together the eggs, melted butter and milk in a jug with a fork. Pour into the centre of the dry ingredients. Mash the banana and add to the bowl.
Stir with a spoon until the ingredients are just combined. Do not over beat the mixture, it should be lumpy at this stage.
Spoon into the muffin cases, filling almost to the top. Bake for 20 to 25 minutes or until the muffins are risen and golden. Allow to cool in the tin for a few minutes then transfer to a wire rack until ready to serve.
The muffins are best served warm.Nutrition information is approximate and is meant as a guideline only.