Lower the spaghetti into a pan of boiling, salted water, stir once, then cook for 5 minutes until al dente or according to packet instructions.
Meanwhile, heat the olive oil in a large sauté pan, with a tight fitting lid. Add the chorizo and fry for a couple of minutes until it has begun to release its oil and has gone crispy. Remove with a slotted spoon, leaving as much of the chorizo oil in the pan as possible, then drain on kitchen paper.
Add the garlic to the pan with the chilli flakes and cook for about 20 seconds, stirring. Add the sherry and allow the alcohol to burn off before adding the passata. Cook for 4-5 minutes until slightly reduced and thickened.
Next add the clams to the pan. Stir well before putting on a tight fitting lid. Allow to cook for 3-4 minutes until all the clams are open.
When the pasta is cooked, drain, rinse briefly and add to the tomato mixture (you may need to add a little of the pasta water if the pasta is a little dry). Next stir in most of the crispy chorizo, reserving some for garnish. Add the rocket then fold everything together until well combined. Divide among warmed wide rimmed bowls and garnish with the reserved crispy chorizo.