Wash the clams under running water then put in a bowl covered with water and leave in the refrigerator overnight, changing the water as often as you can.
An hour before cooking, add a tablespoon of salt to the water to help them  expel any sand.  Drain and wash again.
In a large frying pan, heat the oil, add the garlic and chilli and toss well. When softened, add the clams and wine, cover with a lid and toss over high heat until they open. Give the pan a few good shakes to distribute the heat.
Meanwhile cook the spaghetti in a large pan of rapidly boiling salted water until “al dente”, about 7 – 8 minutes.  Drain. Turn the spaghetti into a large serving bowl, add the clams and toss well, adding plenty of freshly chopped parsley and the lemon juice and zest. Season to taste.