Mix the lemon juice and zest with the Limoncello and set aside.
Gently whip the cream with the sugar until soft peaks begin to form.
Add the lemon mixture and whisk gently until it is all mixed in.
Divide the mixture between six glasses or serving dishes.
Refrigerate until ready to serve.
Just before serving, scatter the syllabubs with the blueberries and crushed biscuit crumbs. You can also garnish with a bit of lemon zest if you like.