Heat the oil in a frying pan. Add the garlic and cook for about 30 seconds. Add the tomatoes and parsley. Cook, stirring from time to time, for about 10 minutes, until broken down and reduced.
Stir the capers, olives, anchovies and chilli powder into the sauce. Season with freshly ground black pepper and cook for a further 5 minutes.
Meanwhile, cook the spaghetti to pack instructions, then drain. Combine with the sauce and scatter the basil over the top.