This series consists of papers relating to Nicholson's involvement in organisations whose principal roles and interests lie outside nature conservation and ecology.

Political and Economic Planning (PEP) material includes a notepad used by Nicholson at the 'original meeting' of the PEP in April 1931, correspondence and other papers concerning its founding and early years, and papers and correspondence appertaining to the 'System Group' which met under the auspices of the PEP to follow up ideas in Nicholson's book The System. Other bodies with which he had significant associations include Dartington Hall School and Trust, Idea-Systems Group ('think-tank' for synthesising existing ideas and knowledge) and the Silver Jubilee Walkway Trust.