Brush the skin liberally with oil so that as the pork cooks, this will render the fat out and help it to blister

Season with salt

Score the skin with a sharp knife to help the fat escape during cooking, but don't cut all the way into the meat.

Pat skin dry then rub with salt and oil to help the fat render and the skin to puff and crisp.

Weigh joint and roast the meat for 25 mins at 240C/fan 220C.

Then turn the oven down to 190C/fan 170C and roast for 25 mins per 450g/1lb.

Rest the meat for 10-15 mins before carving.