Pour boiling water over oats in a large bowl; let soften, about 1 hour. Add treacle, butter and yeast; mix well. Add flour, 1 scoop at a time, mixing well after each addition until dough sticks together. Cover with a tea towel and let rise in a warm place until doubled in volume, about 1 hour.
Grease two 1 lb loaf tins.
Punch down dough and turn onto a lightly floured surface. Shape into 2 balls and let rest for 10 minutes. Form balls into loaves and place in the prepared tins. Cover loaves with a damp tea towel and let rise until doubled in volume, about 30 minutes.
Preheat oven to 190 C / Gas 5.
Bake loaves in the preheated oven until tops are golden brown, about 40 minutes.