Add all the the remaining ingredients to the pan, apart from the spaghetti. Bring to the boil, then lower the heat and simmer gently for 15 to 20 minutes.
When the sauce has been cooking for 10 minutes, start to cook the spaghetti. Bring a large saucepan of water to the boil, add the pasta and bring back to the boil. Stir well and cook for 8 to 10 minutes, until tender.