Place the lemonade, Pimms, sugar and lemon juice in a pan and bring to a simmer. In the meantime, put the gelatine in ice cold water. Once the pan has come to the boil, remove from the heat.
Remove the gelatine from the water and squeeze out any excess water. Stir it slowly into the Pimms mixture until it's dissolved. Leave to cool slightly.
Pour a 10ml layer of the Pimms mixture into a jelly mould and put in the fridge to set.
While you're waiting for the jelly, quarter the cucumber lengthways and remove the seeds. Dice and place on kitchen paper to remove any excess moisture. Repeat this with the apple and grapefruit.
Place a layer of cucumber in the jelly mould. Pour in a little more jelly to cover and put back in the fridge to set. Repeat this process with the rasberries and mint, followed by the apple and grapefruit, and finally a mix of what's left. Chill until thoroughly set.