Like other reviewers here, I saw this back in 1970 when young and impressionable, and had retained memories of it-unfortunately, seeing it now on TPTV is an experience that is-so far-embarrassing at worst but compelling at best! My mother (ex Ultra and SHAEF) disliked it intensely; my father (ex RAF Morse code operator) was less demanding and loved it-I shall stay the course to form my own opinion compared to theirs all those years ago.
The writing is variable from profound to excruciating (witness the early episode 6 when the three are holed up in an empty house). The great and much-missed Peter Barkworth seems often embarrassed; the Alfred Lynch character is laughable and usually deeply annoying-not only to his fellow travellers but to the hapless viewer; Cyd Hayman is beautiful but that cannot sustain one's belief in her character; I await Robert Hardy-even 50+ years on, I still remember being impressed by his performance-let's see if it is as impressive now...
I can forgive the obvious English outdoor locations, but not the ridiculous method the three have of traversing those endless fields!
What is interesting is the remarkably earthy language, some scenes and attitudes-have we moved on in a positive sense, or does viewing this now show how anodyne and "woke" TV has become?
Anyway, once again we can only thank TPTV for giving us the opportunity to assess this series again. (I write this after seeing Episode 6, so may revise my overall critique at journey's end...)