Preheat the oven to 180°c (160 °fan/ Gas 4/ 350F) and grease and line a 2lb loaf tin with baking paper or non stick parchment paper.
Coat the blackberries in the plain flour and set aside.
In a large bowl, cream together the softened butter and caster sugar until pale and fluffy.
Beat in the eggs.
Fold in the self-raising flour, ground almonds, and lemon zest.
Spoon half the mixture into the loaf tin.
Gently fold the flour-coated blackberries into the remaining cake mixture, taking care not to crush them, then spoon it into the tin and level the top.
Bake in the oven for 1 hr 10 minutes, or until a skewer comes out clean (without raw batter on it).
Mix together the caster sugar with enough lemon juice to make a runny drizzle and spoon it over the top of the cake whilst still warm.
Leave the cake to cool before removing from the tin and slicing.
