To make the bases:
Place 8 metal ring moulds of approximately 6-7 cm diameter on a baking tray. Combine together the biscuit crumbs, lemon zest and melted butter. Divide the mixture between the moulds and press firmly into the bases. Chill well whilst preparing the filling.

To make the filling:
Soak the gelatine in a bowl of cold water until softened, then drain well. Meanwhile heat 75 ml of the cream until warm in a small saucepan. Bring almost to the boil and add the tea bag. Leave to infuse for 10 minutes before discarding the teabag. Add the soaked gelatine and stir until melted. (You may need to reheat the cream a little). Whip the remaining cream until thick. Mix together the Philadelphia and sugar until smooth. Gradually whisk the tea flavoured gelatine cream into the Philadelphia mixture and then fold in the whipped cream. Gently fold in about three quarters of the blueberries. Allow the mixture to thicken slightly, until the blueberries are held in suspension, before dividing the mixture between the ring moulds. Refrigerate for 3 hours to set.

To decorate:
Just before serving, remove the cheesecakes from the moulds by warming the moulds slightly with a warm damp cloth and pushing gently up from the bottom. Decorate each cheesecake with any remaining blueberries and a light dusting of icing sugar.