Simmer redcurrants in a pan with a little water until the fruit bursts.
Strain the fruit through a jelly bag into a bowl overnight.
Boil the measured juice with 450g of sugar per 600ml of liquid for 10 minutes.
Preheat your oven to 190°C.
Boil citrus juices and zest, then simmer with port, vinegar, and spices for 20 minutes.
Add 300g of the redcurrant jelly to the spiced liquid and simmer for 10 minutes.
Mix honey, sugar, thyme, redcurrant juice, and mustard to create the glaze.
Score the ham in a diamond pattern and rub the glaze into the surface.
Roast the ham for 50 minutes while basting periodically.
Cool the ham to room temperature before slicing and serving with the jelly.