Add the baking Powder to the flour and sift together into the mixture.
Add the lemon zest and mix it through thoroughly.
Add 3/4 of the blueberries and squish them into the cake mixture.
Dust the remaining whole blueberries in flour and mix into the cake gently, distributing them throughout.
Transfer the mixture into a lined, greased loaf tin and place into the oven at for 40 minutes. Check it is cooked through by poking a knife into the cake, if it comes out clean, it's done. If not, give it a little longer and check again.
Once the cake is cooked through, remove from the oven and pierce several times with a fork.
Mix 1 Tbsp of Lemon juice with the caster sugar and pour over the cake.
Allow to cool completely.
Mix the other 2 tbsp of lemon juice with the icing sugar and drizzle over the cake, allow to set before serving.