Line a bowl with a square of muslin. Wash the 750g (1lb 10oz) oranges and 1 lemon. Cut in half and squeeze out the juice. Place the juice in a pressure cooker and the pips into the muslin lined bowl.
Scoop out any remaining flesh with a teaspoon and add to the pips in the bowl.
Cut the orange shells in half again. Divide into two or three batches and chop in a food processor using the pulse button.
Place the chopped peel in the pressure cooker and add 300ml (½ pt)water. Tie the muslin up into a bag containing the pips and flesh and add to the pan.
Close the pressure cookery and bring up to high pressure. Once the pressure has been reached set a time and cook for 12 minutes. Remove from the heat and allow the pressure to release slowly.
Remove the lid. Lift out the muslin bag and squeeze as much as you can out of the bag by pressing between two saucers.
Add 1 kg (1lb2oz) preserving or golden granulated sugar and heat gently stirring until the sugar has completely dissolved.
Once the sugar has dissolved, increase the heat and bring to a rapid boil. Boil for 10 minutes then test for a set by placing a small spoonful of marmalade on a cold saucer and allowing to cool. The marmalade will wrinkle when pushed with your finger once setting point has been reached. If a set has not been reached then boil for another 5 minutes and test again. Repeat until a set is reached.
Remove from the heat and allow to stand for about 15 minutes.
Stir again then pot into sterilised jars. Seal and allow to cool.
Once open refrigerate and use within 3 months.Nutrition information is approximate and is meant as a guideline only.