Writing partners Terrance Dicks and Malcolm Hulke were famously not enamoured with producer Derrick Sherwin’s decision to exile the Doctor to Earth, and a big part of the success of Season Seven comes down to their attempts to push the boundaries beyond simple alien invasions or mad scientists. With Sherwin gone, Season Eight has felt like a snowballing attempt to revert to an earlier, less restricted concept of Doctor Who. In that sense, Colony in Space feels like the upshot of what Dicks and Hulke have been aiming to achieve.

It also means that the opening scene of the Time Lords discussing the Doctor’s exile comes across as a wry comment on the show’s production office: 

TIME LORD 1: The Doctor resents his exile bitterly. Do you think he’ll co-operate with us?
TIME LORD 2: I doubt it. We immobilised his Tardis, took away his freedom to move in space and time.
TIME LORD 3: Then we must restore his freedom for as long as it serves our purpose.

Watching Colony in Space, I’d be amazed if neither Dicks nor Hulke had ordered up a copy of An Unearthly Child to remind themselves how the series originally handled the TARDIS leaving present-day Earth. So much of this feels like an homage to that original journey. Jo’s amazed “bigger on the inside” reaction to the TARDIS (the one thing we didn’t get from The Claws of Axos) is the first time we’ve had this kind of scene since The Tomb of the Cybermen (Zoe smuggled herself inside), and the technobabble-mocking ‘dimensionally transcendental’ line is a brilliant way to handle it.

But the way Jo’s surprise turns to fear as the TARDIS unexpectedly takes off feels like an echo of Ian and Barbara. And the TARDIS’ arrival in a wasteland, observed by a baffled “primitive” local, is pure Cave of Skulls. Just as he did back in the Hartnell days, the Doctor carefully checks the atmosphere readings, and takes a look at the scanner. When Jo still holds back, the Doctor encourages her, ‘That’s an alien world out there, Jo. Think of it… Let’s find out. Don’t you want to set foot in another world?’ has a hint of the first Doctor’s discussion with Ian: ‘If you could touch the alien sand and hear the cries of strange birds and watch them wheel in another sky, would that satisfy you?… Now, see for yourself.’ And then, just like in The Cave of Skulls, the TARDIS doors open directly out into another place and time, and the travellers step out.

What they find is another small group of human beings struggling to survive in a hostile environment. This time it’s 25th Century colonists rather than cavemen, and Hulke drops in some juicy hints about what they’re running from – not an ice age, but an age of global catastrophe, over-population, pollution and overweening capitalism. But there are also monsters – giant reptiles (although the one we see looks pretty docile), strangely painted telepathic natives, and vicious-looking robots. The last time the show tried anything much like this was The Krotons. There’s something magical about watching the Doctor and Jo – no UNIT, no backup – striding out into the unknown. And, given the show is, again, being reformatted around him, Pertwee looks in his element.

Next episode: Colony in Space – Episode Two