Put the lamb in a large saucepan with the onion, vegetable stock and some seasoning. Bring to the boil over a medium heat, then reduce the heat to a simmer and cook for 2 hrs 30 mins-3 hrs. Turn the heat off, then skim off any scum that has risen to the surface.

Remove the lamb from the pan and leave until cool enough to handle. Cut the meat off the bone and set aside. Add the potatoes, carrots and swede to the pan of stock, and return to the heat. Bring to a simmer and cook for 25-30 mins until just tender. Stir in the leeks and cooked lamb, then cook for a further 5 mins until the leeks are tender. Serve in bowls with a scattering of parsley.