Brian Clemens

Born: July 30, 1931;

Died: January 10, 2015.

Brain Clemens, who has died aged 83, was an exceptionally prolific screenwriter whose successes included the innovative and popular series The Avengers and The Professionals.

The Avengers, which originally featured Patrick Macnee as the dandyish John Steed and Honor Blackman as the leather-clad Cathy Gale, was quirky, witty and occasionally surreal. It was also a popular success, running for six series throughout the 1960s, a decade the style of which it arguably helped to define. It also made a star of Diana Rigg as Emma Peel, who replaced Cathy Gale as Steed's sidekick. In the mid-1970s, Clemens revived the show as The New Avengers, in which Macnee was paired with Gareth Hunt and Joanna Lumley.

In 1977, Clemens produced his other huge small screen hit, the action series The Professionals, which dealt with the fictitious security service CI5 and starred Lewis Collins and Martin Shaw as a pair of tough-guy agents under the command of Gordon Jackson. Though critics were sniffy about the show, which was relentlessly violent, sexist and unsubtle, it ran for 57 episodes and is still regularly - indeed, constantly - repeated.

The origins of The Avengers had little in common with the series that eventually emerged. It was originally devised as a vehicle for Ian Hendry, who had recently starred in a programme called Police Surgeon. That was not a hit, but Hendry's character was popular, and The Avengers was intended to centre around a similar role, with Steed featuring as a sidekick. Clemens was approached to write the pilot episode, Hot Snow, and worked on other scripts before production of the first series was interrupted by a strike. Hendry chose to work on feature films, and the pairing of Steed and Cathy Gale was moved to the fore.

Clemens became the main driving force for the programme when it moved from videotape to film, with which he already had extensive experience, having worked as a jobbing writer for the prolific but shoestring American producers the Danzinger Brothers.

"Before they built their own studios they would go from studio to studio just occupying the space," he explained in an interview in 2009. "They might find that they'd just finished a French chateau film there, then down on the next stage they'd find a submarine or something like that. So they'd come to me and say: 'We want a movie, 80 minutes long and it must have the Old Bailey, a French chateau and a submarine in it!'"

Brian Horace Clemens was born on July 30 1931 in Croydon, the son of an engineer who also worked in music halls; Brian was also the great-great-nephew of the American writer Mark Twain (Samuel Langhorne Clemens), after whom he later named his two sons.

He had pneumonia as a child, and was regarded as delicate, but formed an ambition to write at an early age. His father encouraged him by giving the boy a manual typewriter, which remained his preferred means of production: "Writing is a solitary profession, and the sound of the keys is a great comfort."

He left school at 14, hoping to become a journalist. But despite a spell as a copy boy on Fleet Street, his lack of qualifications held him back. In later life, he credited his period in national service with transforming his character. He served as a weapons instructor with the Royal Army Ordnance Corps, where he learned to ride a bicycle and became something of an athlete.

After turning down a job with a private detective agency in Leeds, he joined the advertising agency J. Walter Thompson as a messenger boy, and worked his way up to a position as a copywriter. He sent his first script, Murder Anonymous, to the BBC, and received an invitation to lunch at the studios. On his arrival, he was told that his work showed promise, but would cost a fortune to film. "So I went away and wrote a play about two men in a railway carriage."

Valid for Single Journey Only was screened in 1955, and brought Clemens to the Danzinger brothers' attention. For the next few years he churned out scripts for low budget feature films and for television series such as Mark Saber (which sometimes involved writing and shooting two episodes a week) The Man from Interpol, and The Invisible Man. For ITC, he wrote the pilot and several episodes of Danger Man, which featured Patrick McGoohan as a secret agent who was a sort of precursor for his character in the cult show The Prisoner.

During this period, Clemens's output was so productive that he often resorted to pseudonyms for his scripts. The success of The Avengers brought him into the production side of the business, and a string of Ferraris followed. Through the Sixties, his tongue-in-cheek caper scripts were in demand for programmes such as Adam Adamant Lives! (the BBC's answer to The Avengers) and - under the pseudonym Tony O'Grady - for Terry Nation's adventure series The Baron.

In the early Seventies, he wrote for Lew Grade's big budget action series The Persuaders!, which starred Roger Moore and Tony Curtis, and devised (though he did not write) a Bafta-award winning sitcom, My Wife Next Door. Between 1973 and 1978 he wrote the vast majority of the six seasons of Thriller for ITV, and began writing for American programmes as well.

After The New Avengers (1976-77) and The Professionals (1977-1983), he worked on episodes of Bergerac, the detective series with John Nettles set on Jersey, and the US comedy crime drama Remington Steele (1982-87), which made Pierce Brosnan a star. He also worked on Perry Mason, Diagnosis Murder, with Dick van Dyke, and the inept BBC science-fiction series Bugs.

He also kept his hand in with scripts for feature films, many of them for the Hammer studios. Among the best of those were Dr Jekyll and Sister Hyde (1971) and Captain Kronos: Vampire Hunter (1974); in the same year as the latter, he wrote The Golden Voyage of Sinbad, the second of the three Sinbad films which featured Ray Harryhausen's stop-motion effects.

See No Evil (1971) starred Mia Farrow as a blind woman, and The Watcher in the Woods (1980) was a ghost story featuring Bette Davis and David McCallum. Less happily, he wrote the story, though not the script, for Highlander II: The Quickening (1991), generally reckoned one of the worst films ever made.

Brian Clemens was appointed OBE in 2010.

He and his first wife Brenda married in 1956 and were divorced ten years later. He then had a decade-long relationship with the actress Diane Enright, who committed suicide in 1976. In 1979 he married again, and had two sons, Samuel Joshua Twain Clemens, an actor and director, and George Barnaby Langhorne Clemens, an editor and director. They and his wife Janet survive him.

ANDREW MCKIE