Preheat the oven to 180°C / Gas mark 4. Line a muffin tin with 10 deep paper cases.
Place the wheat bran in a large bowl with the buttermilk, egg, sunflower oil, raisins, treacle and orange rind. Allow to stand for 10 minutes to allow the flavour to develop.
Sieve the flour, bread soda and cinnamon into a separate bowl and stir in the sugar. Add the dry ingredients to the buttermilk mixture, and quickly fold in until just combined, being careful not to over-mix. Spoon into the paper cases and bake for 15-20 minutes until well risen and golden.
Leave the muffins to cool in the tin for 5 minutes, then serve while still warm.