Heat the oven to 160C, 325F, gas.
Place a sheet of foil lengthways in a roasting tin and another piece widthways across. Put the gammon in the middle of the foil and bring up the edges of the foil to enclose the gammon loosely, leaving room for air to circulate around the gammon.
Cook for 30 minutes per 450g|pound. Remove from the oven. Increase the oven temperature to 220C,425F, gas 7. Open the foil and remove the skin with a sharp knife, leaving the fat intact. Score the fat with the knife to make a diamond pattern.
Discard the foil.
Spread the mustard over the fat and press the sugar all over the top. Stud with cloves. Cook for 25-30 minutes until the glaze is golden. Remove from the oven and leave to rest for 25 minutes.