This is probably the Mud Island to which pinkpercy is referring: (however it's not a seaside resort so is not the one needed as the answer in the quiz)
Quote: "In the late 19th century attempts were made to develop industry on Hornchurch marshes. The Rock Portland Cement Co., Mud Island, was formed 1880, later becoming the Rainham Portland Cement Co. During the 1890s there was also a chemical factory on Mud Island, owned by H. Button & Co."