You need:
1.6kg-ish of pork - shoulder bone-in is best but I can never find bone-in and I don't see why leg wouldn't work
2tbsp salt
2tbsp dark muscovado sugar
1tbsp smoked paprika
2tsp liquid smoke (if you are fancy, I've never used this!)
Preheat oven to 220C. Line a roasting tin with sheets of foil large enough to fold over the top of the pork, then pat the meat dry with a paper towel and add to the tin. Mix the salt, sugar and paprika together and rub half into the meat.
Put the pork into the hot oven for 40 minutes until well browned, then take out and turn the heat down to 125C. If you're using liquid smoke pour it over at this point. Fold the foil over the top to make a sealed parcel and then cook for 6-7 hours (if you have a thermometer the internal temperature should measure 89C). Pour off the juices and reserve.
Turn the heat back up to 220C and cook the pork, uncovered, for ten minutes to crisp up. Take out, cover with foil and rest for 30 minutes.
Using two forks (or your fingers) pull the meat into shreds and add the rest of the seasoning and the meat juices and stir through. Leave to soak for 24 hours (if possible, overnight will do though) before reheating in a warm oven to serve (we like it with white rolls, BBQ sauce and coleslaw).