Line a 1kg/2lb loaf tin with parchment and preheat the oven. Sieve the flour and baking powder into a bowl, stir to combine and set aside.
Put the butter and sugar into a mixing bowl and beat together until light and fluffy. Finely grate the lemon rind, add it to the bowl and beat it in.
Squeeze the lemon juice into a jug, add water if necessary to make it up to 75ml and set this aside for the syrup.
Beat the eggs one at a time, into the mixing bowl ensuring each is well incorporated. Add the prepared flour to the mixing bowl followed by the milk and stir to combine.
Tip the mixture into the prepared loaf tin and smooth the top. Bake for 40-45 minutes until cooked. Leave the cake in its tin.
Put the sugar into a saucepan, pour on the reserved jug of lemon juice and bring to the boil shaking the pan occasionally. Simmer gently for 2 minutes to make a syrup.
Prick all over the surface of the warm cake with a BBQ stick or skewer, pressing right through to the base of the cake.
Pour the syrup slowly all over the surface of the cake and leave to cool in the tin.
Place a chopping board over the cold cake tin and invert it onto the board. Remove the parchment paper.
Using a zester, peel some strands of zest from the lemon and set these aside. Squeeze the lemon juice.
Measure the sugar into a bowl, add the lemon juice and stir to make the drizzle. Pour the drizzle over the top of the cake and spread it around the sides of the cake with a knife.
Scatter the prepared strands of lemon zest over the cake. Leave to set before serving.