Cut the rind from the lemon and squeeze the juice. Peel and crush (mince) the garlic. Mix all the marinade ingredients in a bowl and rub into the outside of the pork. Cover and leave for at least two hours (preferably overnight) in the fridge, to absorb all the flavours.
Place the pork in a lightly oiled ovenproof dish, add the cider and cover. Roast in a preheated moderately hot oven (Mk 6 - 400ºF - 200ºC) for 2 hours, then remove the cover and continue roasting for a further 30 minutes to brown the outside.