These days, Doctor Who has a pretty relaxed stance on altering past events. William Hartnell's First Doctor might've asserted that "you can't rewrite history – not one line" back in the show's early days, but since then we've been educated on fixed points in time and how most of what's already happened is really quite malleable, actually.


All the same, when viewed with a critical eye there are certain aspects of the show's internal chronology that just don't quite hold up – perhaps the most famous example being "UNIT dating controversy" (no, you clever clogs at the back, this isn't a reference to some 1970s scandal involving Mike Yates taking Jo Grant out on the town).

It's all rather complicated but in simple terms there's a question – and indeed some quite fierce debate among Doctor Who fandom – as to when the stories featuring paramilitary organisation UNIT are set. Some argue they take place roughly around the time they were aired, from the late 1960s onwards, while others maintain that they're set at a point further in the future – and indeed, there's on-screen evidence to support both sides.

To give just one example, in 1983 story Mawdryn Undead, the returning Brigadier Lethbridge-Stewart (Nicholas Courtney) claims he retired from UNIT in 1976. Lethbridge-Stewart first appeared in 1968's The Web of Fear – a sequel to the previous year's The Abominable Snowmen, which is clearly stated as having taken place "over forty years" prior... except The Abominable Snowmen was set in 1935, which means The Web of Fear is set at least in 1976, the same year that The Brigadier is said to have retired in Mawdryn Undead.

There's a plethora of clues – from fashion to currency to nods towards politicians of the day – all presenting conflicting options as to whether the UNIT stories take place in what was then present day or the near future. It's a big old muddle which, if you're feeling cynical, you can put down to production errors arising from stories being produced decades apart and which, if you're feeling generous, you can try and explain away using the get-out clause that, well, Doctor Who is all about time travel and so maybe some events got shifted about in history somehow.

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All of which brings us to 2021 and the show's latest episode, Survivors of the Flux, which it has to be said takes an already rather complicated and convoluted question and throws yet another spanner in the works.

One of the episode's plot threads involves space crook The Grand Serpent (Craig Parkinson), who has used his ability to time travel to insert himself into Earth's history and, more specifically, to ensure he's a pivotal player in the early development of UNIT, allowing him to rise to a position of power which ultimately enables him to shut the organisation down, leaving the planet unprotected from a Sontaran invasion fleet.

In scenes clearly labelled as being set in 1958, General Farquhar (Robert Bathurst) announces he's been assigned to set up "the British end of a new United Nations taskforce" – except UNIT doesn't make its first appearance in Doctor Who until a story called The Invasion, which is said to have taken place four years after The Web of Fear, which as we previously established must take place in 1976 at the earliest, meaning The Invasion is set around 1980.

Doctor Who - The Invasion
Doctor Who - The Invasion (1968) BBC

Maybe it's a complex job launching an outfit like UNIT and it takes Farquhar and "Prentis" 22 years – between 1958 and 1980 – to get the whole thing up-and-running? Except in later scenes featuring the pair that take place after UNIT has been formed, the date is clearly advertised on-screen as being 1967, nine years before The Web of Fear – which doesn't feature UNIT and is set before it's established – takes place.

If we ignore the on-screen evidence suggesting that The Web of Fear is set in the mid-to-late 1970s and assume instead that it's set around the same time it was filmed – sometime in 1967 – and that UNIT had already been in operation for around four years by the events of The Invasion, then the scenes featuring Farquhar and the Grand Serpent at the Ministry of Defence just about fit – except a certain cameo throws everything out of whack again...

As Farquhar and Prentis stroll through UNIT headquarters, we hear a familiar voice – that of Brigadier Lethbridge-Stewart – off-screen, putting in a call to the RAF. "That's our new Corporal," says Farquhar. "Brought him in after we missed the whole thing at the Post Office Tower. He’s a shouter, but he’s very good. Keeps everyone on their toes."

It's a fun, fond nod to a much-beloved character – not to mention a reference to 1966 story The War Machines, which saw a hyper-intelligent computer called WOTAN launch an assault on London from its base in the Post Office Tower. But there's a big continuity problem here...

Doctor Who - Mawdryn Undead (1983)
Doctor Who - Mawdryn Undead (1983) BBC

Quite simply, if we assume that UNIT follows the same ranking system as the British army, there's no way that Lethbridge-Stewart should be a Corporal at a point in time after he's been enlisted by UNIT – regardless of when the stories were supposed to be set, he was introduced as a Colonel in The Web of Fear, which takes place pre-UNIT, so why would he now hold the lower rank of Corporal?

Possibly he was demoted from his officer rank as a result of as-yet-undisclosed events which occurred off-screen, but Farquhar seems to speak of Lethbridge-Stewart as a rising star rather than a soldier operating under a cloud – and he's certainly been promoted to his familiar rank of Brigadier by the events of The Invasion, which is a small leap from the rank of Colonel but a much larger one from serving as a Corporal.

If you've lost track of what this all means, well... we can't entirely blame you. But essentially, Doctor Who has now suggested that Alistair Gordon Lethbridge-Stewart was variously a Brigadier serving in UNIT, an ex-Brigadier now retired from UNIT, and a Colonel not serving in UNIT because it didn't exist yet... all in 1976. (Oh, and he was also a Corporal in 1967, after he was a Colonel.)

Oh look, let's just blame Swarm / the Flux / the Division for all of this, shall we? Doctor Who might makes mistakes from time to time, but at least the very nature of the show always gives it an out.

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