Bring the water, vinegar, sugar, star anise, cinnamon sticks, allspice berries, lemon zest, cloves and juniper berries to the boil in a large, lidded, non-reactive pan.
Add the pears, then cover the pan with a lid and reduce the heat until the mixture is gently simmering. Simmer for 10-15 minutes, or until the pears are tender. Remove the pears from the poaching liquid using a slotted spoon and set aside.
Return the poaching liquid to the boil and boil for 4-5 minutes, or until the volume of liquid has reduced and thickened.
Divide the poached pears between two 1.5 litre/2 pints 13fl oz sterilised airtight jars. Pour half of the reduced cooking liquid into each jar, making sure the spices are evenly distributed between each jar. Add one sprig of rosemary to each jar. Seal the jars tightly. The pickled pears can be stored for up two months, but can be eaten after one week. Once opened, store in the fridge and eat within two weeks.