Mix together the Pimm's, confectioner's sugar, citrus juices, half of the mint and the cucumber in a bowl. Blast in microwave for 30 seconds at a time until the sugar is melted. Leave to infuse for as long as you can, then strain.
Stick two ladyfingers together with strawberry jam. Dip into the juices, then arrange ladyfingers around the sides and bottom of a trifle dish. Repeat with remaining ladyfingers. Pour the rest of the syrup over the top and leave it to soak.
Slice some of the strawberries in half lengthways, and place them in a circle around the dish above the layer of ladyfingers. Chop up the rest of the strawberries and place them on top. Pour the custard over the berry layer.
Blend the heavy cream and a dash of Pimm's until soft peaks form. Top the trifle with the whipped cream.
Pick off small mint leaves and pop them on top to garnish. Chill in the fridge for 3 hours before serving.