Place the loin of bacon in a pan of water. Bring to the boil, then reduce the heat and simmer gently for 20 minutes per 450g.
Set the oven to 180ºC (350ºF/Gas 4). Drain the loin of bacon and then score the fat in a diamond pattern. Spread over the mustard. Mix together the sugar and cloves in a small bowl and sprinkle all over the mustard in an even layer. Roast for 20 minutes until the top is nicely glazed and the joint is completely cooked through. Leave to rest in a warm place for 10 minutes.
As soon as you have popped the bacon into the oven, steam the potatoes for 15-20 minutes until just tender. Cook the frozen peas in a separate small pan for 3-4 minutes until just cooked through. Drain the peas and then return to the pan. Season and then add the butter and milk. Blitz with a hand blender until you have a smooth purée. Mash the potatoes until very smooth, then fold in the pea purée until well combined. Season to taste.
Carve the loin of bacon into slices and arrange on warmed plates with the pea and potato mash. Serve with a dish of baby leeks.