Rinse clams under cold water and combine with wine in a medium saucepan with a tight-fitting lid. Bring to the boil, cover and steam for about five minutes or until the clams have opened. Discard any clams that don't open. Strain clams over a large bowl and reserve 1/4 of a cup of the cooking liquid.
Melt margarine in a saucepan and cook the onion stirring until soft. Add bacon and celery and cook, stirring, for five minutes.
Add flour, cook, stirring, until the mixture thickens and bubbles. Gradually stir in stock, undrained tomatoes, potatoes, bay leaves, thyme and water. Cook covered, stirring occassionally for about 15 minutes or until potatoes are tender.
Just before serving, add clams, reserved cooking liquid and parsley to the chowder and stir until heated through.