Put the water, sugar and glucose in a pan and bring to the boil. Simmer to make a syrup. Leave to cool.
Liquidise the lychees with the syrup and strain through a fine sieve. Add the lemon juice to taste.
Freeze in an ice cream machine and make according to the manufacturer's instructions. Alternatively put the mixture into a plastic container and place lid over it.
Leave in the freezer checking and stirring the mixture periodically to create sorbet consistency.