Preheat the oven to 180°C / 350°F / Gas mark 4.
Rinse and dry the ham and then wrap in parchment paper then kitchen foil making sure the fat faces up.
Place on a wire rack set in a rimmed baking tray or roasting pan and roast for 1 hour and 30 minutes.
Meanwhile, grate one third of the horseradish into a bowl with the honey, allspice and some salt and pepper then set aside.
Remove ham from oven and unwrap. When cool enough to handle, peel fat rind from ham with a paring knife, trimming fat all over leaving a thin layer.
Pat dry with kitchen paper. With the tip of the knife, score the skin deep parallel evenly into a diamond shape and return to oven for 30 minutes.
Baste with the honey-horseradish mixture and continue to bake, basting every 30 minutes for about 2 hours more.
If necessary, add water to the pan, about a little water if necessary to prevent the pan from burning and tent with foil if the ham begins to take on too much colour.
Stir together crème fraiche, the remaining horseradish, thyme, and shallot.
Season with salt and pepper.
Transfer the ham to a serving platter and allow to rest at least 20 minutes before serving with horseradish cream.