You might check the files of the British Government (stored in London or available online through a database) to see if they made any observations about Sino-Swiss relations.
I am working on a book project (Habilitation) on Sino-Swiss relations in the Cold War. I am particularly interested in the use of Switzerland as a hub for Chinese business, diplomatic, propaganda, and intelligence networks. Unfortunately, I began my research after the Foreign Ministry Archive restricted access to its holdings.
In preparation for an online update of the Encyclopedia of U.S. Intelligence (Taylor and Francis, 2014), a call for papers is being issued. A comprehensive reference work that examines U.S. intelligence practices, history and education, the Encyclopedia of U.S. Intelligence has been designed to be holistic in nature and examines intelligence issues, practices and history from both academic and practitioner perspectives.