Preheat the oven to 190ºC, 375ºF,Gas mark 5. Wrap the chipolatas in streaky bacon. Roll each slice of bread with a rolling pin to flatten and cut in half. Spread with mustard paste and roll each bacon-wrapped sausage up in each halved slice of bread. Place seam-side down on a baking sheet and brush with butter. Bake in the preheated oven for 20 minutes until golden. Serve hot.