Combine potatoes, onion, celery, 1 cup of the clam juice, 1 cup water, thyme, butter, Worcestershire, salt and pepper to taste in stockpot or Dutch oven. Heat to boiling, stirring often. Reduce heat. Simmer until potatoes are soft, about 20 minutes.
Stir in clams and cook 5 minutes.
Add remaining 4 cups clam juice and cream. Heat to a simmer, about 10 minutes. Do not boil.