Wash the clams thoroughly. Discard any clams that do not close when tapped.
Heat one tablespoon of the oil in a deep, wide pan and, when hot, add the clams. Cover with a lid and cook, shaking the pan occasionally, for 3-4 minutes, or until the clams have the opened. If very few are open, cook for one minute more. Discard any clams that have not opened.
Remove the clams from pan, place into a large bowl and keep warm.
Add the remaining three tablespoons of oil to the pan and add the garlic and tomatoes. Cook very gently, add any juices from the clams in the bowl and season with salt and freshly ground black pepper. Bring to the boil then reduce the heat and simmer for 20 minutes.
Add the clams and chopped parsley and stir.
Add the spaghetti to the tomato and clam sauce and stir to coat the spaghetti in the sauce.
Serve in warm bowls.
