preheat the oven to 220degc/fan 200degc/gas 7. rub the pork with the vegetable oil and sprinkle it with salt. place it in a large roasting tin and roast in the preheated oven for half an hour. turn the oven down to 160degc/fan 140degc/gas 3, cover the tin and the pork with foil, then roast for another 4 1/2 hours.