Place a medium (6- to 8-quart), heavy soup pot over medium-high heat. When hot, add the bacon. When it starts to brown in spots, lower the heat to medium and continue to cook until most of the fat has been rendered and the bacon is almost crisp, about 4 minutes.
Add the vegetable oil, onions, carrots, celery, leeks, and green bell peppers. Sauté, stirring occasionally, until very soft, 10 to 15 minutes. Add the garlic and sauté for another 2 minutes.
Add the diced and puréed tomatoes, bay leaf, thyme, and potatoes.
Add the stock or clam juice to the pot. Stir to mix well. Bring to a boil over high heat, and then lower the heat to a simmer and cook for 30 minutes, stirring occasionally, or until the potatoes are fork-tender.
Add the clams with their juice and season with the salt and pepper. Add the Tabasco and Worcestershire. Bring back to a simmer for several minutes.
Ladle into bowls and serve with crusty bread or crackers.