Preheat oven to gas 7, 220°C, fan 200°C. Rub the lamb shanks with a little salt and pepper, place in a deep roasting tin and cook for 10 minutes. Toss the leeks, shallots and carrots with the olive oil and add to the tin. Return to the oven for a further 10 minutes, until the lamb and veg are starting to brown.
Reduce oven temperature to gas 4, 180°C, fan 160°C. Add the barley, stock, wine (or water, if your prefer) and bay leaves to the tin plus 200ml (7fl oz) of water. Cover with foil and roast for 2 hours 15 minutes, or until the lamb is very tender and the barley has cooked through. (This dish is not quite a stew but it isn't dry, either; there will be some liquid left in the tin after cooking.)
Spoon into shallow bowls and scatter with chopped parsley. Serve with roast potatoes, if desired.
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