Preheat a large griddle pan over a high heat, then add the chillies and cook for 20 minutes, or until blackened all over, turning occasionally. Transfer to a bowl, cover with cling film and set aside for around 10 minutes to cool.
Once cooled, peel and discard the blackened skin, then halve and deseed. Heat a lug of olive oil in a medium frying pan over a low heat, then finely slice and add 2 garlic cloves. Fry for a few seconds, or until lightly golden, then add the chillies and tinned tomatoes, breaking them up with a spoon. Bring to the boil, then reduce to low and simmer for around 5 minutes. Season with salt and pepper, mash well with a potato masher, then set the arrabbiata sauce aside.
Cook the spaghetti according to packet instructions in a large pan of salted boiling water over a high heat.
Meanwhile, pick the parsley leaves and set aside for later, then finely slice the stalks. Halve the squid tentacles, thinly slice the tubes, then finely slice the remaining garlic. Preheat a large frying pan over a medium-high heat, add the parsley stalks, garlic, clams, wine and 2 large spoonfuls of arrabbiata sauce, then stir well. Add the squid and toss well to coat. Cover and cook for 3 to 4 minutes, or until the clams have opened.
Drain the spaghetti, reserving a cupful of the cooking water, then add to the clams. Roughly chop and add the parsley leaves, toss well, adding a splash of the reserved cooking water to loosen, if needed. Stir in any remaining arrabbiata sauce if you fancy more of a kick, drizzle with extra virgin olive oil and serve straightaway.