As Ian put it when he tasted this "I'll never drink ordinary lemonade again". It was very sweet so I might try using a little less sugar next time.
Water - 1 litre
Caster sugar - 225 g
Finely grated rind of 3 lemons
Lemon juice - 250 ml (use 5 large or 10 small lemons)
Blackberries - 300 g
1) Add the sugar and half the water to a saucepan and bring to the boil. Boil for a couple of minutes, stirring occasionally. Add the lemon rind to the pan and leave for a minute. Add the lemon juice and remaining water.
2) Combine the blackberries with 250 ml of the lemon mixture in a blender. Blend and then strain through a sieve to remove the seeds.
3) Pour the blackberry mixture and remaining lemon mixture into a jug and refrigerate until chilled. Serve with ice.