Dissolve the sugar in the water in a saucepan over a gentle heat. Turn up the heat and boil for 1 minute.DO NOT STIR once the sugar is dissolved or the mixture will turn grainy
Pour the mixture into a bowl or jug and cool, then chill in the fridge
Zest and juice the limes and lemons
When the sugar syrup is cold, add the gin, tonic, fruit juice and zest and stir well
Freeze for 2-3 hoursYou don't want it to be frozen solid. If it's too solid, leave to melt slightly
Froth the egg white with a fork or electric mixer on slow
Break up the frozen mixture with a fork and beat vigorously with a fork, electric mixer or in a processor. Add the egg white and give it another blitz
Pour the mixture into a plastic box and freeze until solid