Heat half the olive oil in a paella pan or a large frying pan. Tip in the pork and cook for about 5 mins until lightly browned, but not cooked through. Remove pork from the pan, then set aside on a plate.
Pour the remaining olive oil into the pan, then add in the onion, garlic and chorizo. Cook for about 5 mins until the onion is softened and the chorizo is starting to crisp and give off its oil.
Add the rice and paprika to the pan, then stir around for 1-2 mins until all the grains of rice are well coated. Can be prepared up to this point 1 day in advance and stored in the fridge.
Pour the tomatoes and any juices into the pan along with the pork and 3 2/3 cups of the vegetable stock. Bring to the boil, reduce the heat, then let it gently simmer for about 20 mins until the rice is nearly soft.
Place the spinach in a sieve, then pour over a kettle of boiling water so the leaves are just wilted. Arrange the spinach leaves in the pan along with the clams.
Pour over the remaining vegetable stock, then cook for another 10 minutes By this time the clams should have opened (discard any that haven't) and the rice should be tender. Serve straight away from the pan.