Preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Grease a 10 cup bundt tin with oil or melted vegan butter making sure that you get right into all of the nooks and crannies.
Sift together the flour and baking powder for the orange batter in one bowl, and the flour, baking powder and cocoa powder for the chocolate batter in another.
Add the sugar, oil, orange zest and juice, water and orange extract to the orange batter, and the sugar, oil, vinegar, water and vanilla extract to the chocolate batter.
Stir each with a balloon whisk until no dry lumps remain.
Alternate spooning the batters into the bundt tin then gently run a knife though to swirl them together slightly.
Bake for 40-45 minutes until a skewer inserted into the centre comes out clean.
Allow to cool in the tin for 20 minutes then carefully turn it out onto a wire rack and leave to cool completely before serving.