Production was halted while filming in Ireland. Producer Mahmud Sipra had recently purchased Ardmore Studios just outside of Dublin. The same fate also befell another of his productions due to shoot there too. "The Bengal Lancers" with Michael York, Miles O'Keefe, and Sir Christopher Lee, was also shuttered, due to lack of funds.
Another version of the Burgess, Philby, and McLean story was planned between 1977-1978 with Sir Alan Bates, Robert Shaw, and Vanessa Redgrave starring. Shaw's death, and financing issues, killed the project.
Philip Kimberley (Sir Michael Caine) was based on the double agent Kim Philby. When this was first announced in 1976 with Mike Hodges directing, Philby was aghast at the casting of Caine, and wanted to be portrayed by Trevor Howard.
Indoor scenes were filmed in a disused hanger located at Brooklands Race circuit, Weybridge, Surrey. The site has now been redeveloped. The original hanger was next door to a similar hanger which temporarily housed the TNT freight company's Weybridge depot during the construction of the purpose built depot building on the same site.
The movie starts with a scene in Russia, but was filmed on the main Market Square in Helsinki, FInland. The Orthodox church in the background is Uspenski Cathedral. The Soviet office is actually (and still is) the Swedish Embassy in Helsinki. In the background you see the corner of the Presidential Palace of Finland.