Of particular importance was his work on National Parks. The government's proposals for local government reform threatened to weaken further the already feeble National Park Committees. At the request of his fellow Commissioners, Jack prepared an admirable report outlining the case for stronger park authorities. This provided the arguments with which the Commission was able to strike a deal with the Association of County Councils and the government to strengthen the parks. Jack then served as an active and wise member of the panel, chaired by Lord Sandford, which reviewed policy for national parks. The panel's report provided a stimulus for the work of the parks in the following 15 years.