Cook bacon in a large pot over moderate heat, stirring, until golden, about 5 minutes. Remove all but a film of bacon fat. Reduce heat to moderately low, then add onion, bell pepper and celery and cook, stirring, until softened, about 5 minutes. Stir in potato, bottled clam juice and tomatoes (with juice) and simmer, covered, 10 minutes. Stir in clams and simmer, covered, stirring occasionally, until clams open wide, 10 to 15 minutes. (Discard any clams that after 15 minutes have not opened.) Remove pan from heat.

Remove most of clam shells with tongs, then detach clams and return them to chowder. (Keep a few in their shells for garnish.) Stir in parsley and salt and pepper to taste. Serve.