Wash and pat dry the raspberries. Reserving a few for decoration, push the remaining raspberries through a nylon sieve into a jug to make a purée. Set aside.
Put the Vege-gel in a bowl and blend with 200ml (7fl.oz) cold water. Set aside.
Put the cornflour in a saucepan and blend with a little of the milk to make a paste. Stir in the rest of the milk along with the cream and caster sugar.
Heat, stirring, until the mixture comes to the boil and thickens. Cook for 1 minute, then stir in the Vege-Gel mixture and bring back to the boil.
Remove from the heat, mix in half of the raspberry purée and a few drops of Red Gel Food Colour, if using.
Working quickly, pour the mixture into 4 x 150ml (¼ pt) jelly moulds or ramekins. Allow to cool completely then chill for at least 2 hours.
Mix the remaining raspberry purée with icing sugar to taste, then cover and chill until required.
To serve, dip the moulds in very hot water for a few seconds to loosen the Jellies and invert on to serving plates. Serve with a little raspberry purée spooned over and decorate with the reserved raspberries and mint sprigs.