Mix the flour and suet together in a bowl.
Combine the milk and water together in a jug or separate bowl.
Mix in enough of the milk and water to the flour and suet mixture to make a dough that is soft, but not too soft to roll.
Roll the dough out on a floured surface, to make a large circle. Cut out a quarter of the circle (to be used later as the lid of the pudding).
Grease a 1.5 litre/2¾ pint heatproof basin or bowl. Place the larger circle of pastry into the bowl and join the cut sides together, pressing well.
Place half of the butter cubes and half of the sugar into the bottom of the lined bowl.
Prick the lemons all over with a larding needle or skewer, so the juices can escape, then place the lemons on top of the butter and sugar.
Place the remaining butter and sugar over the lemons to fill the bowl.
Roll out the reserved pastry quarter into a round and place on top of the basin filling. Press the edges together to seal the pudding.
Place a piece of foil over the basin, creating a pleat in the middle. Tie the foil in place with string and tie around carefully to create a string handle over the top, so the pudding can be easily moved when hot.
Bring a large pan of water to the boil and lower the pudding into it. The water should come halfway up the sides of the bowl.
Cover the pan with a lid and leave to simmer for 3-4 hours. If the water level falls too low, replenish it with more boiling water.
To serve, carefully remove the basin from the pan and remove the foil lid. Put a deep dish over the basin and turn the pudding out onto the dish. Place on the table and serve immediately.