Rinse and dry the lamb, make several small gashes in the surface. Place in a bowl. Mix together all remaining ingredients. Pour over lamb and marinate overnight in the refrigerator, basting several times. Drain lamb, reserving marinade.
Spit the lamb securely with a drip pan underneath. Roast for 1 3/4 hours for medium rare meat, 2 1/2 hours for well done. Brush frequently with marinade. Serves 8-12.