Bring a large pot of water to boil for the pasta.
In a large pan with a lid, heat the oil over medium. Add the anchovies and cook until they melt into the oil, 2 to 3 minutes. Add the garlic, spring onion whites, thyme and crushed red pepper. Cook, swirling the skillet occasionally, until the spring onions are tender, 2 to 3 minutes. Add the vermouth.
Meanwhile, salt the boiling water, add the pasta and cook to al dente.
Add the clams to the pan. Cover and cook, shaking the pan occasionally, until the clams open, 5 to 8 minutes (discard any clams that don't open). Uncover, add the butter and swirl the skillet until the butter melts. Stir in the parsley and lemon juice and season with salt and pepper.
Drain the pasta and return it to the pot. Add the clams and sauce; toss 1 minute. Adjust the seasoning and serve immediately.