Sapphire & Steel actually began life as a children's show called The Time Meddlers. Creator PJ Hammond (who had already written for shows including The Sweeney, The Professionals, Z Cars, and the fantasy series Ace of Wands) pitched the series to Thames Television, they were initially interested but for various reasons decided not to develop the series. Hammond then took The Time Menders to a different ITV affiliate, ATV, who were so impressed by the concept and strength of the writing, plus the potential low cost in producing the series, that they asked Hammond to emphasise the creepiness of the series and decided to broadcast the show during prime time hours.
It's amazing to think that ITV, which at the time was very much the home of middle of the road (read that as bland) television, agreed to produce such a unique and mind bending series, and to air it twice weekly (Tuesdays and Thursdays). I suppose ITV must have felt they finally had a series that could give Doctor Who a run for its money. And in ideas, story lines and acting, it certainly did.
The basic show premise was that time is like a tunnel, with different time zones spread along itself. Outside there are dark forces that take advantage of any weakness, enter and wreak havoc. Extra-terrestrial 'Operatives' were assigned by an unknown authority to combat the dark forces. As the show would tell us:
"All irregularities will be handled by the forces controlling each dimension. Transuranic, heavy elements may not be used where there is life. Medium atomic weights are available: Gold, Lead, Copper, Jet, Diamond, Radium, Sapphire, Silver and Steel. Sapphire and Steel have been assigned..."
Sapphire (played by Joanna Lumley) and Steel (David McCallum) took on human form to resolve the problems. Both of them had special powers, Sapphire could rewind time, see the history of an object and control human minds, whereas Steel was very strong, possessed the power of telekinesis and could drain thermal energy. The pair were also telepathic.
Sapphire & Steel boasted intelligent scripts, and dark challenges for the pair of Operatives to tackle. In the first story a time warp develops after the reading of some historic nursery rhymes, this brings Roundhead Soldiers to the 20th Century. Other 'assignments' include an ancient, faceless life form that could exist in photos, a black entity that fed on the resentment of dead World War 2 soldiers, and a foe so deadly that the only way Steel could be rid of the entity was to offer it the soul of a ghost hunter that they had previously befriended. This would prove to be a shocking twist to one of the finest stories in the series, and certainly not the children's show PJ Hammond had originally envisioned.
The superb onscreen chemistry between David McCallum and Joanna Lumley really helped propel the series to greatness. Lumley was perfect at playing the stunningly beautiful character with an odd air of something quite different about her, whilst McCallum played Steel as cold as his name suggests. The magic of the series lies in the fact that very little is revealed about who they are, what they are, or where they are from.
However, ITV panicked when viewers wrote in asking what the series was about (you wouldn't get that with BBC viewers - just saying), and so despite a very strong premise only 6 'assignments' (34 episodes) were produced, which were broadcast over 4 years, from 1979 to 1982, with the last episode not transmitting until two and a half years after it was shot. But this wasn't so much down to ratings as other factors that even two Time Operatives couldn't have controlled. First, there were industrial strikes to deal with, and then the ITV affiliate ATV lost its contract and was replaced by Central Television. Central decided not to make any more episodes, and so Hammond changed the ending of the last story to make it more of a shock.
Epilogue - In 2005 Sapphire & Steel was revived by Big Finish for a new range of audio adventures, starring Susannah Harker as Sapphire and David Warner as Steel. PJ Hammond went on to write for such shows as The Gentle Touch, The Bill and Wycliffe. He was asked to write a story for Doctor Who in the mid 80s, unfortunately this was the year the show went on hiatus and returned with The trial of a Timelord series. His script for the story Paradise Five was eventually produced by Big Finish as part of their Lost Stories series. Hammond also contributed two scripts for Torchwood, Small Worlds and From Out of the Rain.