Heat the olive oil in a large saucepan, add the garlic, lemon rind and anchovy to the pan and cook for 30 seconds, mashing the anchovy lightly so it dissolves into the sauce. Pour in the wine and leave to simmer for a couple of minutes. Add the chilli flakes, tomatoes and clams to the pan. Cover with a lid and leave for 5 minutes until the clams have opened, discarding any that do not open. Add a tablespoon of lemon juice to the pan and season with pepper.
Meanwhile, heat a large pan of lightly salted water until boiling and then add the spaghetti. Cook according to the pack instructions, drain, reserving a little of the cooking water, and return to the pan.
Stir through the clams and any juices with a little cooking water to loosen if necessary, then toss through the rocket just before serving.