Preheat the oven to 200°C (fan oven 180°C), gas mark 6.
Heat a heavy pan without any fat for a few minutes until very hot. Add the duck breasts, skin side down, and cook for 5-6 mins until the skin is crisp and golden brown.
Turn the breasts over and transfer them to a roasting tin. Place in the centre of the preheated oven and cook for about 10 mins. Remove and leave to rest on a warm dish.
While the duck is resting, place the juice and the marmalade in a pan. Heat gently until the marmalade has melted and stir in the oil. Season to taste.
Slice the duck breasts diagonally, place on warm plates and pour over the sauce.
Serve with herby mixed rice, some lightly cooked French beans and fresh peas.