The Secret Service is a 1969 British science fiction television series created by Gerry and Sylvia Anderson and filmed by their production company, Century 21, for ITC Entertainment.

Assisted by fellow agent Matthew Harding, Unwin's missions involve frequent use of the Minimiser, a device capable of shrinking people and objects to facilitate covert operations.

This technique was combined with scale model effects sequences and – uniquely for an Anderson puppet series – extensive footage of live actors in long shot.

Filming began in August 1968 and ended with the completion of the thirteenth episode in January 1969 after Lew Grade, Century 21's owner and financial backer, responded negatively to a test screening and cancelled the production.

He is stationed at his vicarage with fellow BISHOP agent Matthew Harding, who when not assisting Unwin on missions affects a country accent and serves as the Father's verger and gardener.

[14] Anderson remembered Unwin's radio and TV performances using the language and thought that it would suit the character of a secret agent, also reasoning that it would have comic value if shown to confuse the enemy.

"[15] The premise of The Secret Service was inspired partly by the Joe 90 episode "The Unorthodox Shepherd", which features an elderly and seemingly half-deaf vicar who is covering up a money forging operation on the grounds of his church.

[11] For reasons of economy, he eventually opted for a hybrid format that blended scale puppet sequences with footage of live actors filmed in full-sized surroundings.

[11] To avoid the long-running problem of making the puppets walk convincingly, the series often used footage of live actors in long shot for scenes that required characters to move.

[10] Stephen La Rivière notes the contrast between the format of The Secret Service and those of earlier Supermarionation series, whose live-action elements were usually limited to occasional shots of human hands performing actions too complex for the puppets, such as operating machinery.

[18] 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.

"[18] 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.

"[19] 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 as the headquarters of BISHOP.

[17] 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".

This features the title graphic sliding down into view and gradually filling the screen – an effect was inspired by traditional imagery of angels descending from Heaven.

[22] Accompanied by a church organ and percussion instruments, the vocals were intended to be performed by The Swingle Singers, but their prospective fee was too high for the music budget.

Lew Grade, Century 21's financial backer, ordered Anderson to end filming on The Secret Service during a test screening of the pilot episode, "A Case for the Bishop", in December 1968.

[7] Objecting to the series' concept on the basis that American audiences would be confused by the Unwinese, Grade capped the production at the thirteen episodes that either had been completed or were shooting at the time of the screening.

"[29] Of Grade's decision, La Rivière conjectures: "No one knows what was running through [his] mind ... but given the ease with which the 'Unwinese' element could have been removed [from] the series, it seems probable that he simply didn't like a lot of what he was seeing.

Having wanted to abandon puppet work and move into live-action, Anderson greeted the cancellation of The Secret Service with optimism, saying of live actors: "I started to think, 'It's amazing!

The Secret Service captures the English whimsy that was making The Avengers such a hit in America, but adds to it the charm of Four Feather Falls, the irony and wit of Fireball XL5 and the technical accomplishments of the later Supermarionation shows.

"[34] Simon Wickes of the website TVCentury21.com suggests that the series was made primarily to bridge the gap between the Andersons' puppet productions and their later efforts in live action.

Stephen La Rivière favours the episode "More Haste Less Speed": describing the series finale as "wonderfully quirky", he considers the plot about a money-forging scheme to be reminiscent of the "gentler, earlier days of Supercar" and lauds voice actor Keith Alexander for his impression of the elderly Lady Hazlewell.

[30] Ian Fryer of FAB magazine expresses similar views, writing that "very little about The Secret Service has obvious appeal to the traditionally young Supermarionation audience."

He notes that the title sequence marked a departure from Supermarionation's "tradition of having a thrilling or suspenseful promise of what was to come", instead "[making] the series look suspiciously like it might be about the life and work of an elderly vicar."

Fryer also suggests that prospective foreign buyers were put off by the espionage theme, noting that by the time The Secret Service debuted on British TV, other spy series like The Man from U.N.C.L.E.

Writers Chris Drake and Graeme Bassett state that "On paper, at least, the premise seemed irresistible" but view the blending of puppetry and live action as "uneasy".

"[16] La Rivière also argues that another factor contributing to the failure of The Secret Service was the frequent re-runs of earlier Anderson series: "... as with anything that is phenomenally popular, the time must come when the audience is satiated and drifts away to something else.

He judges the combination of puppetry and live action "completely pointless" and the casting of Unwin not only "bizarre in the extreme" but also ill-considered given that Unwinese "was hardly funny to most people (let alone children)."

[44] Reviewing the episode "Recall to Service" for the fanzine Andersonic, Paul O'Brien describes the plot about the AquaTank – a military robot gone rogue – as "an obvious allegory about the hazards of complete automation".