Preheat the oven to 220°C. Rinse the inside of the ducks under cold running water, drain well and pat dry with paper towels. Put a rosemary sprig and one onion half and one orange quarter inside each duck and tie the legs together. Prick the skin all over with a fork or skewer, put the ducks on a rack in a roasting pan and squeeze over the juice from the other orange quarters. Dot the birds with the butter and season with the salt and pepper.
Roast the ducks in the centre of the oven for 15 minutes. Reduce the oven temperature to 180°C and continue to cook for a further hour, or until the ducks are well done. Baste twice during the cooking time and cover with foil if the skin begins to brown too much.
Twenty minutes before the end of the cooking time, start to make the sauce. Heat the oil in a saucepan and cook the onion and carrot gently until the onion is light golden brown. Stir in the flour and cook for 1 minute, then blend in the strained giblet stock and season to taste. Bring to the boil, stirring, then boil gently until the sauce is reduced to 2 cups. Remove from the heat, strain into a clean saucepan and set aside.
Using a vegetable peeler, thinly peel the rind from the orange and cut it into fine shreds with a sharp knife. Remove and discard the pith. Holding the orange over a bowl to catch the juice, cut out each segment by slicing down between the segment and the membrane on either side. Squeeze the juice from the remaining tissue and set the segments and juice aside. Put the shredded peel into a saucepan with barely enough water to cover and boil for 2 minutes. Remove from the heat and set aside.
Carefully transfer the cooked ducks to a heated serving plate, cover with foil and keep warm. Skim all the fat from the rich juices that are left behind in the roasting pan. Heat and pour in the red wine and bring to the boil, stirring and scraping any browned residue off the bottom. Strain through a sieve into the sauce. Stir in the strained orange juice, half the blanched orange rind and the redcurrant jelly. Simmer for 5 minutes, stirring frequently, then stir in the orange segments with their juice and heat for 1 minute. Season to taste.
Spoon a little of the sauce over the ducks as a glaze. Pour the remainder into a sauceboat. Using a sharp knife, cut off the duck legs and carve the breast meat into long, medium-thick slices. Garnish with the remaining orange rind and rosemary sprigs and serve with the sauce, mashed potatoes, green peas and mint jelly.