Season the chicken with salt and freshly ground black pepper. Heat 2tbsp oil in a large frying pan over a high heat and fry the chicken until golden on each side. Transfer to a large saucepan or slow cooker.
Heat the remaining oil in the frying pan over a medium heat. Add the pancetta and cook, stirring occasionally, for 2 minutes. Add the onion, celery and garlic.
Cook, stirring from time to time, for 6-8 minutes, or until the onion is tender. Add the wine and stir with a wooden spoon to incorporate any bits stuck to the pan. Transfer to the saucepan with the chicken. Add the tomatoes with their juice, and the bay leaves and thyme.
Bring to the boil over a medium heat. Reduce the heat, cover and simmer, turning the chicken occasionally, for 25-30 minutes.
Check the sauce and add a little water if necessary, or, if it's too thin, remove the chicken, increase the heat and cook until the sauce has reduced and thickened. Season to taste with salt and freshly ground black pepper and serve with boiled potatoes.
You can Substitute Chicken breasts for legs if you prefer white meat.