Heat half the oil in a large pot and add lamb shanks, cooking until seared all over. Remove from pot. Pour in remaining oil and cook onion an cook onion, carrot, celery and garlic. Cook until onion is just tender.
Return shanks to the pot with the stock, water and herbs. Bring to the boil and simmer covered for approximately 1 1/2 hours until meat is tender and falling away from the bone. Add barley and potatoes to soup halfway through cooking time.
Take shanks from the pot and remove meat from the bones. Shred or dice and return to the pot.
Season to taste and serve with parsley and crusty bread.