Wash and scrub the oranges and lemons, Cut the fruit in half and squeeze the juice out into a large preserving pan. Using your fingers, pull out the membrane and the pips and pile on to a large square of muslin. bring up the corners and tie tightly with string to make a bag then place in the pan,.
Cut the peel into shreds and add to the pan with the water. Bring to the boil, then simmer gently for 2 hours until the contents have reduced by half and the peel is soft and tender.
Remove the bag and place in a colander over a bowl, press out the liquid and, when cool enough, squeeze the bag to get out the essential pectin, which will make the marmalade set. Add the liquid to the pan with the sugar. Stir until the sugar is dissolved, then bring to the boil and boil rapdily until setting point is reached - this might only take couplew of minutes. remove any scum from the surface and cool for 10 minutes before pouring into warmed sterilised jars.
Stir 2 tbsp treacle into the marmalade at the end of boiling for a rich dark flavour.
Add 2-4 tbsp whisky to the mixture just before potting.
Add 100g fiely chopped stem ginger just before potting.