Sprinkle the gelatine over the lemon juice and water in a heatproof bowl and leave to soak for 5 minutes until spongy.

Meanwhile, cut the melon flesh into chunks and work through a nylon sieve, or puree in a blender then sieve to remove fibres.

Pour the puree into a saucepan. Add the sugar and heat gently, stirring constantly, until the sugar is dissolved. Remove from the heat.

Stand the bowl containing the gelatine in a pan of gently simmering water and heat gently for 1 - 2 minutes until the gelatine has dissolved, stirring occasionally.

Stir the dissolved gelatine into the melon mixture, then add enough

colouring to tint it a fairly strong green. Stir in ginger, if using. For a streaky effect, lightly stir in a little extra colouring.

Pour the mixture into a bowl; cool, then cover and refrigerate until beginning to set.

In a clean, dry bowl, whisk the egg whites until standing in stiff peaks. Whip the cream in a separate bowl until it will just hold its shape. Fold the cream and then the egg whites into the melon mixture.

Divide the mixture between 6 individual glasses or glass bowls, cover and refrigerate for 8 hours, or overnight, until set. Serve chilled.