Preheat the oven to 240°C, fan 220°C, gas mark 8. Rub the salt into the scored skin of the pork joint and let sit for 30 minutes.
Using kitchen paper, brush the salt off the pork and wipe dry. Rub 1 tablespoon of the oil into the skin then place the pork into a clean roasting tin.
Cook for 25 minutes and then lower the temperature to 180°C, fan 160°C, gas mark 4 and cook for a further 2 hours.
Meanwhile, scatter the sliced fennel, apple wedges, lemon, thyme and garlic into a lightly greased roasting tin. Drizzle with the remaining olive oil and season. Place on the shelf below the pork, 50 minutes before the end of its cooking time.
For the final 15 minutes of cooking time, increase the oven temperature to 220°C, fan 200°C, gas mark 7 to crisp up the crackling. Remove the pork, and the fennel and apples from the oven. Let the meat rest, uncovered, for 15 minutes.
Snip the string off the pork, slide a knife under the crackling and lift off. Carve 150g meat per person. Serve with the crackling, roasted fennel and apples, mash and apple sauce.
Leftover pork can be cooled, wrapped in clingfilm and stored in the fridge for up to 48 hours.
Cook's tip: For an easy apple sauce to go with the roast pork, peel, core and chop 500g British Bramley apples and place in a pan with 150ml water, 1 teaspoon cider vinegar and 50g sugar. Put the lid on and simmer for 5-8 minutes, stirring often, until the apples are soft. Remove the lid to simmer off any remaining water. Take off the heat and whisk in 25g butter. Keeps in the fridge for 3-4 days.