"Last Train to Bufflers Halt" and "The Cure"). Supporting character voices were provided by all of the regular cast except Unwin, with additional contributions by David Healy and (for the final two episodes, "May-Day, May-Day!" and "More Haste Less Speed") David Graham. Filming After a summer of pre-production, filming began on 20 August 1968. According to director Ken Turner, The Secret Service was difficult to film as it comprised three elements: puppet and effects filming (both conducted in the studio) and location filming. The Secret Service also differed from earlier Supermarionation series in that episodes were structured around their location work, which had to be completed before the studio filming could commence. Turner explained: "We felt that somebody had to take the location stuff by the balls, get it shot and then hand it over to the director to fit his puppet stuff in. I suppose that seemed a bit back to front but with that programme it was what worked out best." Producer David Lane remembered that making the series was "an absolute nightmare" due to the wide range of design scales used: "You can imagine the problems. You're shrinking [the Matthew Harding puppet] to puppet size on a puppet set and then you're having to build it in live-action size for the puppet because he's supposed to be a small man in a full-sized environment. And then you're using the 'shrunken' puppet in a full set." Filming locations included a house in Burnham, Buckinghamshire as Father Unwin's vicarage, Centre Point as the British Intelligence building in London and Horse Guards Parade as the headquarters of BISHOP. Wexham Park Hospital appears in the episode "School for Spies", while the Century 21 Studios themselves, located on the Slough Trading Estate, are featured in the opening of the first episode, "A Case for the Bishop". As the series is set in the then-present day, the special effects team, headed by Derek Meddings, were not required to design many futuristic-looking vehicles. Their main tasks were to build the Ford Model T, Gabriel, create miniature replicas of vehicles and settings common to the 1960s, and produce the optical effects for Matthew Harding's "minimisation". Three versions of Gabriel were built: one full-sized car and two models in differing scales. The car was fitted with belt-driven electric motors, an upholstered interior, a folding roof and a radio control mechanism so that it could be driven