Sift together the flour and baking powder. Set aside.
Cream butter and sugar together until almost white. Add two of the eggs, then 1/2 dry mixture and mix. Repeat, adding the remaining two eggs and the rest of the dry mixture.
Zest and juice lemons and add 3/4 of the zest and juice to the cake mixture. Save the rest for the drizzle. Add mango juice and mix. Combine and if the mixture is dry, add milk 1 teaspoon at a time. Give a final mix and place in a greased and lined loaf tin. Level out using the back of a spoon or spatula.
Bake in a pre-heated 180 C / Gas 4 oven for 20 to 30 minutes, or until golden brown on the outside and a skewer inserted in the centre comes out clean.
Mix icing sugar and rest of lemon juice and zest until it becomes a drizzle. When loaf has cooled, remove from tin and drizzle the lemon mixture on top.