Yet the Professionals not only succeeded in its day but continues to do so in repeat runs almost 25 years on.
Bodie and Doyle's characteristics arguably had near-plagiaristic similarities to that of Starsky & Hutch. The action and (more particularly) violence depicted was essentially a continuation of the "rules" laid down by The Sweeney. Yet The Professionals still carved out a niche for itself. What sets it apart from the other shows is the firework chemistry between the two leads (as much down to the good fortune of casting Shaw and Collins together - two completely different actors) and the jibing, black humour they share and harangue each other with.
Gordon Jackson's searing performance as Cowley, meanwhile, proved to be a formidable boss for the two reprobates.
The humour also extended to the situations and the show was not afraid to make fun of itself occasionally.
In the early years the exciting, varied plots were a bonus, too (Contrary to other remarks, they were often quite complex). Action-wise, Collins and Shaw gamely tackled much of their own stuntwork.
Although characterisation was never the primary objective of the show, the characters were given a reasonable opportunity to add facets to their personae. Doyle, in particular, emerged as a surprisingly rounded, unpredictable and constantly surprising character - due mainly to Shaw's splendid acting skills.
Unlike other British action shows, the Professionals gained an immense female following - indeed its fandom is probably split 50:50 between the sexes.
In the meantime London Weekend Television exported the show massively to eager overseas broadcasters (and continues to do so to this day).
However the programme was not without faults. By the fourth season (1980) the writing team were struggling to find new ideas and the boys of CI5 often found themselves lumbered with jobs that more traditional law forces would normally take on.
By 1981 the show was clearly running out of steam and with Shaw and Collins keen to move on to other things, LWT decided to call it a day after a grand total of 57 episodes.
Today it's easy to say the whole reason it's such a success again is because of its refreshingly un-PC image. Yet there is more to it than that and, indeed, what were seen as the strengths of the show in 1977 are being appreciated by new audiences the world over.