Drain the gammon well and put into a large pan, skin side down. Cover with fresh cold water and add the sugar. Bring slowly to the boil, skimming off the scum as it rises. Lower the heat, cover and simmer for 50 minutes - 1 hour. Top up with extra boiling water when necessary.

Drain the joint. Carefully cut off the rind and score the fat into squares. Wrap the joint in foil, place in a roasting tin and roast at 180°C (350°F) mark 4 for 40 minutes.

Put the marmalade and mustard together in a small saucepan and stir over gentle heat until the marmalade is melted. Remove the gammon from the oven, remove the foil and brush the gammon with glaze.

Raise the temperature to 220°C (425°F) mark 7 and cook uncovered for a further 20 minutes.

Halve the orange slices and arrange them in rows, overlapping slightly, over the gammon. Fasten them in place with cloves. Brush the remaining warm marmalade glaze gently over the orange slices.

Return the gammon to the oven for 10 minutes or until the orange slices are heated through.