‘You can’t have the United Kingdom. There’s already people living there. They’ll think you’re going to pinch their benefits.’ Peter Harness takes the Daily Mail’s nightmare scenario seriously, with a slow invasion of immigrants seeking to maintain their own culture, and then to supplant the indigenous population. The Zygons play into all the stereotypes, with their “community leaders” trying to contain the ‘radicalisation’ of the younger brood but unable to stem the tide, and the gloating Zygonists triumphantly declaring victory in the first battle.

Boldly, the production goes beyond a general alien invasion scenario to dress up the Zygonists in the imagery of Islamist terrorism. Their flag is a black flag with a white symbol and text; they issue videos of terrified hostages; there’s a ‘No British’ sign playing into the right-wing idea of “no go” areas; they’re based in “Arabstan” (sorry, ‘Turmezistan’), clearly some central Asian state about to get bombed by Western soldiers, and the first disguised radicals we meet are posing as an Asian family in London. When this aired, Islamic State was at its height, with areas in Syria and Iraq under their control, “Jihadi John” beheading hostages on camera; gay men being thrown off roofs; women and girls being forced into sex slavery, and the systematic slaughter of Yazidis.

Into these news headlines bursts Doctor Who like John Nathan-Turner doing a story of balaclava-wearing Terileptils with Irish accents phoning in coded bomb warnings. At the time, I watched this like one of the audience of Springtime for Hitler, wondering how on earth a family sci-fi show with some blobby body-snatchers was going to engage with this humanitarian disaster, and doing it in a way that, unlike Harness’ Kill the Moon, avoided glib answers.

It’s not a problem that especially troubles this episode, which is all about the end of days set-up and is mostly an effective thriller. The washed-out colours and real-world settings give it a down-to-earth quality that suits the grim subject matter, and – given they’re ISIS – the Zygonists are portrayed as ruthless murderers, preying on the (implausible) sensibilities of the UNIT troops and the people in Truth or Consequences, reducing their victims to tumbleweed or dumping them in wheelie bins. There is a slightly tasteless moment of the Doctor tap dancing about the cremated remains of Colonel Walsh’s soldiers looking for Osgood, but that’s an outlier. The cliffhanger is the best this series: Jac’s fate is cruel, and Coleman is utterly believable as a cold, superior Zygonist al-Bagh-daddy. But the pay-off is crucial.

Next Time: The Zygon Inversion