Objectively, the toy tank is far from the worst effect we’ve seen over the last few serials, but the problem is it hits you right at the top of the episode before you’re ready for it, and as it’s gently pushed into view by Clifford Culley’s hand it’s hard not to smirk. Which is a shame, because again Terrance Dicks has gone to great lengths to make sure this should be affordable and achievable (the much-vaunted Giant Robot is in it for less than five minutes of this episode), and Barry Letts has arranged for it to be all made on videotape to avoid a repeat of the floaty dinosaurs.

There are loads of good things about the episode. The nuclear countdown is tense – Hilda Winters, whose failure to return in The Sarah Jane Adventures is a rare misstep by RTD, is a properly hissable, mad-eyed villain, like a British Home Secretary delighting in their latest crackdown on asylum seekers. She’s so smug that even the usually gallant Brigadier snaps and yells at her. This, appropriately enough, was one of the earliest Tom scenes I saw as it was included in a BBC Schools programme in the 1980s. There are some more self-aware moments of comedy (‘Just once I’d like to meet an alien menace that wasn’t immune to bullets’) and the King Kong pastiche is charming. The Robot itself is a great design, and Michael Kilgariff’s histrionic performance is hilarious: most brilliantly when the Robot has just shot Kettlewell, and throws its hands in the air theatrically declaiming, ‘I have killed the one who created me!’ as if it’s in a play wot Ernie wrote.

But… it’s an oddly low-key, almost throwaway introduction for the new Doctor, typified in the cursory and overly-signposted resolution (Kettlewell’s mention of a metal-eating virus is as basic as the reptile-killing hexachromite gas in Warriors of the Deep). The Power of the Daleks pitted Troughton against the show’s biggest draw. Spearhead from Space gave an indication what the new, Earthbound format was going to be like. This doesn’t do either. There’s a “business as usual” tone to it that’s understandable – they don’t want us to doubt the new Doctor, so his post-regeneration settling in is essentially confined to the first episode and afterwards everyone just acts pretty much as if nothing’s happened. Plus, with a new production team (Philip Hinchcliffe and Robert Holmes) coming in, presumably Letts and Dicks don’t want to saddle them with too many impositions in the way Derrick Sherwin foisted a limiting reformatting on them. In a marked departure from Sarah Jane’s introduction, they don’t even bother to give the new male companion a proper character. The end result is a story that exists in a sort of limbo, not really much like a Pertwee serial, but nothing like a Tom Baker story.

Next episode: The Ark in Space