After a decade in development, plans to transform a historic military site into 635 homes are coming to fruition. Fort Halstead, at Halstead near Sevenoaks, sits on the crest of the North Downs, making it the ideal defensive position to protect London in the event of foreign invasion. At least that was the thinking of the Secretary of State for War, Edward Stanhope, who commissioned the fort to be built in the late 1890s. Since then, it has seen life as the secret establishment for early work on the development of Britain’s nuclear bomb, delivered to the Royal Air Force in 1954, and more recen…