2U.K.If within six months from the passing of this Act the Authority notify the Concessionaires that they have decided to proceed with the construction of a public sewer and other works for the improvement of drainage sufficient to provide for the disposal of surface water from the terminal area at Cheriton, Folkestone and that it is their intention to complete the works within the period of three years thereafter, the Concessionaires shall not, so long as the Authority proceed with the construction of those works in accordance with that intention, construct the drainage lagoon (Work No. 16) and, on the completion of those works, the powers of this Act for the construction of the lagoon shall cease to have effect.