I did a roast pork joint for dinner today - it was a 2.6k piece of meat. I cook it for 30 mins per lb/500g plus an extra 30 mins. I cook it on full whack to crisp the (salted. peppered & covered in lemon tyme) crackling for the first half hour & then turn it down to gas mark 7 (200?) for the rest of the time with foil on top until the last 3/4 hour.
Like piggling said DON't double the time - you'll end up cremating it all! Give it maybe an extra half an hour to an hour basting it often but check to see if it has clear juices running when stabbed with a knife.
Tip: you could take the rind off completely, salt/season it and cook it separately to the pork meat.
good luck
hth