Line a 20cm springform cake tin with baking parchment. Combine the digestives and butter in a bowl and mix well. Press into the base of the prepared cake tin.
Combine the mandarin orange segments in a food processor (reserving a few segments for decoration) with the sugar and lemon juice and blend until smooth. Transfer the mixture to a clean saucepan. Soak the gelatine leaves in cold water for 5 to 6 minutes. Squeeze out any excess liquid then add to the mandarin purée and warm over a low heat until dissolved.
In a large mixing bowl, whisk the double cream until light and fluffy, then mix in the cream cheese. Gradually add the mandarin purée mixture and whisk until light and airy. Spoon into the prepared cake tin and smooth over the biscuit base. Gently smooth the top of the cheesecake. Chill in the fridge for 6 hours or overnight.
Remove the cheesecake from the fridge and carefully pop out of the cake tin and place on a serving plate. Arrange the reserved mandarin segments on top of the cheesecake to decorate and serve.