For the jelly, place the redcurrants into a pan with a little water, bring to a simmer and cook until the fruit bursts. Tip into a jelly bag and strain overnight into a large bowl.
Next day, measure the juice, place in a pan and add 450g/1lb of preserving sugar for every 600ml/20fl oz of juice. Dissolve the sugar over a high heat and boil for 5-10 minutes then remove the pan from the heat.
Preheat the oven to 190C/375F/Gas 5. Place the orange and lemon juice and zest in a clean pan, bring to a boil then reduce the heat and add the port, wine, vinegar and spices. Simmer for 20 minutes then add 300g/10½oz of the redcurrant jelly mixture and simmer for a further 10 minutes. Remove the pan from the heat and set aside to cool.
For the ham, mix together the honey, sugar, thyme, redcurrant juice and mustard to make the glaze. Slash the surface of the ham in a diamond pattern and rub in the glaze. Place the ham in a roasting tin and roast for 40-50 minutes, basting from time to time.
Allow the ham to cool to room temperature then cut into slices. Serve with the jelly, chunks of bread and a celery, apple and fresh parsley salad.