Dust the chicken thighs with the seasoned flour to coat lightly.
Heat half the oil in a flameproof casserole, add the chicken, in 2 batches, and cook over a medium-high heat for 5 minutes until browned on both sides. Remove from the pan with a slotted spoon.
Reduce the heat to medium and add the remaining oil to the pan. Add the onion, carrots, celery, garlic and salt and pepper to taste and cook, stirring frequently, for 5 minutes. Add the wine, stock, rosemary and lentils and return the chicken thighs to the pan.
Bring to the boil, stirring, then reduce the heat, cover and simmer gently for 1½ hours until the vegetables and lentils are tender.