Drain the lychees, reserving the syrup. Top the syrup up to 250ml (9fl oz) with water, then put the syrup, lychee juice and sugar in a saucepan. Bring to the boil, reduce the heat and simmer for 5 minutes.
Soak the gelatine leaves in a bowl of cold water until soft, then squeeze them to remove excess water, add to the hot syrup and stir to dissolve. Strain into a jug and mix in the Prosecco.
Pour a small amount of jelly into the base of 6 Martini glasses. Place in the fridge and allow to set. This should take around 2 to 3 hours.
When the jelly has set, divide the lychees among the 6 glasses, along with a sprinkle of glitter on each. Divide the remaining jelly equally over the top of the lychees and put in the fridge for a further 4 hours until set.