Warm the stock and add the saffron. Set aside to infuse.
Heat the oil in a large deep pan, and brown the chicken thighs on all sides.
Remove from the pan and put to one side.
Lower the heat, add the onion and peppers and cook for 5 mins. Add the chorizo, and cook for a further 2 mins until the chorizo has released some of its oils into the dish. Add garlic and cook another minute.
Add the vermouth and bring to a boil to cook off the alcohol (about a minute).
Stir in the tomato paste and paprika.
Return the chicken pieces to the dish along with the parsley and stock. Bring it to a boil, cover the dish with a tight-fitting lid and lower the heat. Cook for 30 mins.
Add the rice and stir everything together. Cover, and simmer for a further 15 mins, or until the rice is cooked and has absorbed most of the cooking liquid. Remove from the heat and leave the dish to sit for 10 mins to absorb any remaining liquid.