Set oven to 425F/Mark 7. Cut the sausages into 2-3 sections and fry gently in a pan until browned. Transfer to a dish and keep warm.
Fry onions and bacon until soft, add the flour and fry for 1 minute. Add the tomatoes, tomato puree, sauces and stock, season and bring to the boil, stirring. Add mushrooms and sausage pieces, simmer for 15-20 minutes, then transfer to an ovenproof dish.
Meanwhile, make the scone topping. Sift the flour, salt, baking powder and mustard into a bowl and rub in the butter. Add the egg and stir in sufficient milk to mix to a soft dough. Roll out to 1/2in thickness on a floured surface, cut into small scones with a cutter, and arrange, overlapping, around the edge of the sausage mixture in the dish. Bake in oven for about 15 minutes until the scones are risen and golden brown.