"Jason King" was always an anticlimax after "Department S". Both were made at Elstree Film Studios with many of the same personnel, but "Jason King" was shot on 16 mm rather than the 35 mm of the earlier series and in 1971 the difference was jarringly obvious. Despite a few foreign location shots (mainly King crossing a road in Berlin or Paris) the whole thing looked decidedly cheap.
"Department S" had the great hook of a bizarre pre-credit incident and much of the interest was in discovering the rational cause. The Jason King character was a gadfly with unpredictable, often wrong, flashes of insight. Stewart Sullivan and Annabelle Hurst could be left to do, respectively, the gumshoe and the brain work. King was best taken in small doses which worked in "Department S" as he did not have to carry the plot. However, as the lead character in his own series he was in virtually every scene and had to be sensible and motivated enough to do the traditional detective stuff in order to progress the stories (which were themselves (unlike "Department S") little different to those of a dozen other series).
The tension in the one character between the frivolous dilettante and the determined detective often willing to risk his life for others must have been difficult to reconcile and the tone of the scripts and the degree of King's flamboyance varied significantly from episode to episode. King also suffered from not having strong regular characters the equal of Sullivan and Hurst to bring him down to earth when necessary and balance his excesses. The more interesting episodes were those rare ones where King was angered by the real suffering of others and had to confront, if not the hypocrisy, at least the irony of, his usual moaning about the minor irritations of his luxurious lifestyle.
Extracting King as a character from Department S was an example of an often repeated mistake in TV. Because a character is hugely popular in one situation it doesn't follow that they will work outside their complex support structure of setting, format, other characters, style, etc. (Having Inspector Morse star, in an Australian-set, pseudo-western rather than an whodunnit in Oxford is another example which fortunately only happened in one episode) King might have become even more of an unlikely heartthrob in his own series but the drama suffered badly.
Having said all that, "Jason King" remains a far more interesting, entertaining and original series than most and Peter Wyngarde (view "Night of the Eagle" to see him at his very best) one of the more complex and electric performers let loose in the lead of a major TV series. It is just that coming at the tail end of the "golden era" of ITC filmed series it is difficult not to judge it by higher standards than usual.
