Place an ovenproof saucepan or casserole dish over a medium heat and add a dash of oil. Once hot, add the pancetta, a little pepper and the chilli and fry until cooked through but not crisping. Add the garlic and cook for 2 minutes, then add the onion and cook over a low heat until completely tender, about 5 minutes. Stir in half the sugar, then add the vinegar. Boil for 1 minute, then add Worcestershire sauce to taste.