Pre heat oven to 150 degrees.
Heat oil in a large stove proof baking dish, and fry the shanks for 10-15 mins, or until well browned all over. Remove to a plate.
Turn heat down to low. Add leeks and fry for 1-2 mins or until they begin to soften. Add garlic and herbs and fry for a further minute.
Add flour and stir for 1 min.
Then add wine, stirring to scrape the bottom of the pan and bring to a simmer. Add stock, lamb and any lamb juices and bring to the boil.
Cover tightly with foil and cook in oven for 4 hours, turning every hour until meat is tender and falling away from the bones.
To thicken the sauce remove shanks from sauce and keep warm. Simmer the sauce in the dish over medium heat until reduced slightly. Add shanks back to sauce if serving in baking dish.