Heat oven to 160°C/gas 4. Line the base of a 23cm springform cake tin with greaseproof paper. Crush the biscuits to fine crumbs in a food processor, tip into a bowl and combine with the melted butter. Press the crumbs down evenly over the base of the tin, place in the oven to bake for 10 mins until lightly brown and crisp on top. Remove and allow to cool.
Put one third of the blueberries into a saucepan and add 3 tbsp water, 175g of the sugar and the zest of 1 of the limes. Cook for 2 mins or until the berries start to ooze. Leave to one side to cool. Strain the juice into a small pan, set aside, and keep the berries.
Make the filling. Mix the cream cheese, sour cream and double cream with the remaining sugar, lime zest and all the lime juice until smooth. Add the gelatine to 3 tbsp cold water in a cup, leave until it begins to look spongy, and then dissolve until clear by standing the cup in a pan of water over a low heat. Combine a little of the creamy mix with the gelatine and then pour into the rest of the mixture ensuring to beat well.
Fold the cooled berries gently into the creamy mixture; this will create a ripple effect. Pour onto the biscuit base and place in the fridge to chill for at least 4 hours, or until set.
Meanwhile, heat the rest of the juice for 2-3 mins until slightly syrupy. Stir in the remaining uncooked berries and leave to cool. When set, carefully remove the cake and slide onto a plate. Spoon the syrupy berries on top.