Combine the crushed tomatoes, molasses, soft brown sugar, mustard powder or mustard, water, salt and pepper in a medium saucepan. Bring to the boil and stir until the sugar has dissolved. Remove from the heat and set aside.
Finely slice bacon and put into a large casserole dish. Drain the haricot beans and add them to the dish. Add the tomato mixture, stir to combine and then cover.
Bake for 6 hours.Check every hour to ensure there is enough liquid around the beans and add water if necessary.