The night before baking the bread prepare this starter: In a medium sized non-metal mixing bowl, dissolve 1/2 teaspoon yeast in 225ml warm water. Add 200g flour and mix well. Cover and let sit overnight at room temperature.
The next day: In a large mixing bowl, dissolve 1 dessertspoon yeast in 450ml warm water. Add the starter mixture, wholemeal flour, 200g flour and salt; stir until well combined. Add the remaining flour, a little at a time, mixing well after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 8 minutes. Lightly oil a large bowl, place the dough in the bowl and turn to coat with oil. Cover with a clean damp cloth and let rise in a warm place until doubled in volume, about 1 hour.
Grease two 23x12cm (9x5 in) loaf tins. Deflate the dough and turn it out onto a lightly floured surface. Divide the dough into two equal pieces and form into loaves. Place the loaves into the prepared tins. Cover the loaves with a clean damp cloth and let rise until doubled in volume, about 45 minutes. Preheat the oven to 220 C / Gas mark 7.
Bake in the preheated oven for about 30 minutes or until the top is golden brown and the bottom of the loaf sounds hollow when tapped.