In a small bowl, dissolve the yeast and sugar in the warm water. Let stand until creamy, about 10 minutes.
Combine buttermilk, butter, honey and the yeast mixture in a large bowl. Add the salt, all of the seeds and the wholemeal flour. Stir to combine. Add the bread flour, 60g or so at a time, mixing well with a wooden spoon after each addition. When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 6 minutes.
Lightly oil a large mixing bowl, place the dough in the bowl and turn to coat with the oil. Cover with a clean damp cloth and put in a warm place to rise until doubled in volume, about 1 hour.
Preheat oven to 190 degrees C. Grease two 23x12cm 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 with a clean damp cloth and let rise until doubled in volume, about 40 minutes.
Bake for about 30 minutes or until the tops are brown and the bottom of a loaf sounds hollow when tapped.