Rinse the clams and mussels under cold running water. Place in a bowl of salted cold water and leave for about an hour. You will notice the shells opening slightly. Rinse under cold water again.
Meanwhile bring a saucepan of slightly salted water to the boil. Add the pasta and cook until al dente. Drain and set aside.
Place the rinsed clams and mussels in a large saucepan together with the wine, garlic, oil and parsley. Cover with a lid and cook on a high heat for three minutes, until all the shells have opened.
Remove the clams from the heat. Immediately discard any unopened shells. Remove two-thirds of the clams and mussels from their shells, leaving the rest intact. Set aside.
Strain the cooking liquor through a fine sieve to remove any impurities. Return the cooking liquor to the pan with the shelled clams and mussels and cook on a medium heat until it reduces slightly.
Stir in the saffron, tomato and chilli then season to taste with salt and freshly ground black pepper.
Add the drained pasta to the sauce.
Mix in the rocket and season with salt and freshly ground black pepper.
Remove from the heat and stir in the clams and mussels in the shell. Drizzle with oil and serve immediately.