Slash the skin of the duck in a diamond pattern, using a sharp knife. Heat a heavy frying pan until very hot, add the duck, skin side down, and cook over a high heat for 8-10 minutes, turning once, until browned and cooked but slightly pink inside.
Remove the duck from the pan to a warm place. Drain off the fat from the pan, leaving a thin coating. Add the shallots and turnips and stir over a moderate heat, for 2-3 minutes, until golden, then add the garlic.
Add the wine and lemon zest and simmer for about 1 minute, then cover and simmer, stirring occasionally, for 10-12 minutes or until the turnips and shallots are almost tender. Stir in the lemon juice, honey and sage and cook for a further 4-5 minutes, until caramelised and tender.
Add the duck breasts, with skin removed if desired, and cook for 1-2 minutes, spooning the juices over the duck. Add salt and pepper to taste. Remove to warmed plates, spoon the vegetables around and serve with steamed potatoes and spinach.