I've just started reading Timeless Adventures: How Doctor Who Conquered TV by Brian J Robb, and quickly concluded just how fortunate we Whovians are that the programme was made at all.
It seems that the old-guard at the BBC of 1963 were determined for Doctor Who to fail, and only for it's defenders, Sydney Newman, Verity Lambert et al, then the embryonic show would have fallen at the first hurdle.
Fast forward to the first Dalek story's transmission, and the powers-that-be thankfully reacted by abandoning the show's intended 13-week lifespan.
Only after reading the production notes on The Rescue DVD this week did I learn that by August 1964, Donald Baverstock again wanted to revert the Doctor Who contract to just 13 weeks, and cancel the show when all remaining stories finished in January 1965.
Only when Lambert and William Hartnell's agent dug in their heels did Baverstock finally agree to another, 26-week run, by which time the programme's long term future was secured. The threat of cancellation would however revisit the programme in times of crisis. As The War Games concluded the black & white era in 1969, the BBC considered a 6 year run to have been a good innings and there was some internal debate about whether to axe Doctor Who. The lowest point in the show's history was the 'hiatus' of 1985 when Michael Grade 'rested' the Doctor's adventures for 18 months, then the end finally arrived in 1989 with outright cancellation.
It's hard to believe that the programme could have ended after serial K (ie. just 51 episodes), and was so close to becoming a footnote in TV history.