Place the lamb in a large, lidded roasting dish. Make incisions in the meat with a sharp knife and insert a garlic sliver and rosemary sprig into each incision. Season. Roast the lamb in a preheated oven at 220?C, 425F, gas mark 7 for 20 minutes, then reduce to 180?C, 350F, gas mark 4. Lightly fry the onion, carrots, celery and leeks in the oil for 5 minutes. Add the stock and wine and bring to the boil. Season with pepper and add the sprigs of thyme. Pour around the lamb, cover tightly and cook, basting occasionally, for 3 hours. Remove the herbs from the stock, then remove the lamb, cover with foil and leave to rest. Transfer the vegetables and stock to a saucepan. Add the redcurrant jelly, beans and tomatoes and simmer for 5 minutes. Carve the lamb and serve on a bed of the vegetables with creamy mashed potatoes. NOTES : British lamb is perfectly complemented by garlic and rosemary. Braising the lamb with the vegetables in stock keeps the meat moist and full of flavour.