In the film, Whale make the statement that you won't need a surge damper. I'm not sure that is true;-
Where you have a storage water heater, they invariably have a non return valve fitted to their cold water input port. This means that the hot tank will fill to the cold water pressure, but as the water is heated, the water expands, and consequently will raise the pressure in the hot system.
When any mixer tap is opened, the increased pressure in the hot tank will feed the tap, and prevent the cold water pressure dropping, delaying the point when the pump will run. Consequently you may get a slug of hot water before the cold water pump turns on.