Soak the beans overnight in plenty of fresh cold water. Drain and rinse, then put in a heavy, ovenproof pan or casserole, with fresh water to cover the beans by about 5cm (2in). Bring to the boil and boil briskly for 10 minutes. Remove scum. Lower the heat and simmer gently, covered with a lid, for about 45 minutes until the beans are tender but not completely soft.
Snip the bacon into pieces and dry fry with the onion until onion is tender. Add to the beans with the tomato purée, brown sugar, black treacle, mustard, Worcestershire sauce and garlic. Season with black pepper.
Bring back to the boil and simmer for a further 30 minutes until the beans are meltingly tender.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.