Add the gelatine leaves to a bowl and cover with cold water. Leave to soak for 5 minutes.
Add the Pimms to a small saucepan and heat on a very low heat while the gelatine is soaking. Squeeze out the gelatine leaves and add to the saucepan. Stir with a balloon whisk until the gelatine has dissolved. Add ginger ale and lime juice.
Split the strawberries, raspberries, cucumber, mint and mandarin between the 4 serving dishes. Pour over the pimms jelly mixture.
Leave the jelly to set in the fridge and serve.