One of British television’s finest achievements in the 1960s was The Avengers which ran for 161 episodes across six series between 7 January 1961 and 21 April 1969. Created by Sydney Newman who, later that year, would leave the independent ABC (where he created The Avengers) for the BBC where, as Head of Drama, he would set in motion the chain of events that would lead to Doctor Who (1963-1989), The Avengers was a follow-up, though not a sequel, to an earlier Newman series, Police Surgeon (1960). In that show, Ian Hendry had starred as the eponymous Dr Geoffrey Brent and although it lasted for only 13 episodes, Newman decided to keep the star on as the lead in his new programme.

Now playing Dr David Keel, Hendry was initially the star of what was, for its first series, a fairly straightforward crime drama. Keel’s fiancée, office receptionist Peggy (Catherine Woodville), is murdered by a gang of drug dealers in the first episodes, Hot Snow, and the grieving Keel is approached by a stranger, John Steed (Patrick Macnee) who is investigating the dealers. Steed needs Keel’s help and offers him a chance to avenge Peggy’s death (hence the otherwise slightly inexplicable title) and their partnership is so successful that they decide to stay together to investigate other crimes. Sadly, all but three of these early episodes were junked and it’s often forgotten that the series had more mundane routes, non-fans only really being aware of how strange the show would become as it went along.

The first hint of that strangeness came in the second series. Hendry was gone, off to pursue his burgeoning film career, and Macnee was promoted to series lead, aided and abetted by a rolling trio of assistants – the almost forgotten Dr Martin King (Jon Rollason) who only appeared in three episodes, amateur sleuth and nightclub singer Venus Smith (Julie Stevens) and most importantly, anthropologist and judo expert Dr Cathy Gale played by Honor Blackman. It was the relationship between the no-nonsense Gale and the old-school English gent Steed that would cement the winning formula that would see The Avengers through its glory years.

And those years would come in 1965 with the arrival of both Mrs Emma Peel (Diana Rigg) and later, colour. The series had become one of the first British shows to shown on prime-time US television and the money that brought in enabled ABC to start shooting ion 35mm film. The programme was now as far from the original conception of it as it was possible to be. Steed had long since abandoned his trench coat in favour of chic Savile Row tailoring, the gritty, two-fisted drama of the first series had been transformed into something more elegant and witty and the relationship between Steed and his female partners was refreshingly non-sexual and entirely professional, though tinged with a genuine love and respect.

It was the two series that Steed adventured alongside Emma Peel that remain the most popular. The scripts – by the likes of Brian Clemens, Malcolm Hulke, John Lucarotti , Roger Marshall and so many others- were wittier (in the episode Too Many Christmas Trees (25 December 1965) Steed gets a Christmas card from the now departed Cathy Gale and he wonders why she’d sent it from Fort Knox; on leaving The Avengers, Blackman had fought alongside James Bond at the military base in Goldfinger (1964)), the action more exciting (Peel was as likely to pitch in and beat up the bad guys as Steed, if not more so, a revelation in the mid-60s) and the stories more outrageous.

Science fiction ideas had skirted around the Avengers for some years, but the time Mrs Peel was on board, they were coming to dominate. She and Steed battled the robotic Cybernauts (The Cybernauts (12 October 1965), Return of the Cybernauts (27 September 1967)) and Christopher Lee as Professor Frank N. Stone in Never, Never Say Die (15 March 1967); struggled with killer plants in Man-Eater of Surrey Green (7 December 1965), an invisible man (The See-Through Man (30 January 1967) and a killer who murders with his electric touch (The Positive Negative Man (1 November 1967)); and had their minds and identities stolen (Who’s Who??? (27 September 1967)) and end up being miniaturised by an experimental ray beam (Mission… Highly Improbable (15 November 1967)).

It’s all gloriously silly stuff, as wild and psychedelic as anything else that was going on in Britain at that time (The Avengers are as much an integral part of the 60s as The Beatles). There had been little quite like it before and it’s the endlessly inventive situations, the witty banter and the unforgettably mad villains that helped to ensure the public’s continuing love affair wit the series. Rigg left at the end of episode one of the sixth and final series, The Forget-Me-Knot (25 September 1968), handing over the duty of care for Steed to Tara King, played by Linda Thorson. Thorson is often given a hard time but in fairness, she’s not that bad at all – she’s just not Diana Rigg who was so magnificent as Mrs Peel that anyone would have struggled by comparison.

But the writing was on the wall for The Avengers. The writers introduced Patrick Newell as a semi-regular “handler” for the duo, Mother, but the plots were never quite as interesting or daring, though the series came to its final end in the perfectly titled Bizarre (17 May 1969) with Steed and King being fired off into space, Mother breaking the fourth wall to assure us that they’d be back. That wouldn’t quite happen – though Steed would return later – and the series bowed out and into television legend.

At its best – and that accounts for much of its run – The Avengers was hugely entertaining madness, set in an odd little never-never world even then, such that although some of the references and a good deal of the fashions have dated, much of what makes it fun still works today. Macnee’s peerless performance as the suave Steed is the very antithesis of James Bond – never womanising, moved to violence only when necessary and the very epitome of English gentlemanliness. His colleagues – and they were colleagues, every bit Steed’s equal, not just sidekicks or eye candy for the dads watching – were all terrific. Mrs Peel is everyone’s favourite, thanks to Rigg’s marvellous performance, but Gale and King have more than their share of charm too.

The series became so ingrained in the public consciousness that a follow-up series was possible seven years later. Macnee returned as Steed in The New Avengers (1976-1977), once again tackling odd adversaries like giant rats, ex Nazis and even the Cybernauts across two series with Joanna Lumley and Gareth Hunt as Purdy and Gambit making up the rest of the new team. It was great fun too, though it never quite captured the high weirdness of the original. The less said about the disastrous big budget Hollywood feature film version, The Avengers (1998), directed by Jeremiah Chechik and starring Ralph Fiennes and Uma Thurman as Steed and Mrs Peel, the better. It had the mad plot (to control the world using a weather manipulating machine) and Sean Connery as the villain, but absolutely everything that we knew and loved from the small screen incarnation is entirely missing. In Germany, the Avengers, which was broadcast on many stations around the world, was retitled Mit Schirm, Charme und Melone, which translates as “With Umbrella, Charm and Bowler Hat” which pretty much sums up the show really. It’s uniquely British in its eccentricity yet has enough universal appeal to make it a hit around the world and across generations. Could such a show work again today? Maybe not. It seems very much of its time, very much the product of a decade when the British creative scene was enjoying a new-found sense of confidence and adventurousness thanks to the global success of The Beatles. In the right, sympathetic hands, something similar might work. But it could never be The Avengers.