Set a fine mesh colander over a bowl and drain clams into the mesh. Reserve clam juice and set juice and clams aside.
Heat a heavy bottomed soup pot or Dutch oven over medium high and add the bacon. Cook stirring occasionally until crisped. Remove bacon from the pot and drain on a paper towel-lined plate. Set aside.
Add leeks to the residual bacon grease and saute for about 5 minutes, until soft. Add celery, carrots and thyme and continue cooking for another 3 minutes.
Add clam juice, including the clam juice reserved from the canned clams, chicken stock and Worcestershire sauce. Bring to a boil and add the potatoes. Return to a boil and then reduce heat to medium low. Add the bacon and crushed red peppers to the pot and cook until the potatoes are tender, about 15 minutes.
When potatoes are done, stir in 4 tablespoons of butter. Add clams, lemon juice and parsley and heat briefly. You do not want to overcook the clams or they become tough and rubbery. Taste and adjust seasonings.