This is a thoroughly grim episode. The opening battle sequence goes on for ages, and oddly benefits from Richard Martin’s slapdash direction because it looks genuinely chaotic and shocking, with explosions going off, and people running in all directions. It works really well. So does the later (film) sequence of Barbara, jenny and Dortmun’s desperate race across London, with the classic images of Daleks outside the Palace of Westminster, in Trafalgar Square and outside the Albert Hall.

Bernard Kay really sells the aftermath of the failed attack: resigned and weary, he’s thoroughly shattered by what he’s seen. Ann Davies is also good as Jenny – so brittle, using cynicism as a weapon to stop anyone getting too close. A shell shocked man, his mind broken by the horror, is abandoned in the resistance base while outside Baker, who’s just reunited the Doctor and Susan, is gunned down by the Daleks, and Dortmun sacrifices himself in a futile attack on another Dalek squad to buy Barbara and Jenny a chance of escaping the doomed London. It’s a really dark episode.

Which makes the humour all the more important: the Dalek confronting a dummy in the transport museum, and David cleverly flattering the Doctor into doing what he suggests. Hartnell’s performance in this scene has such a flavour of Tom Baker’s it’s hard to believe he didn’t see this: ‘Yes, I think it’s a very good idea,’ says the Doctor accepting the credit, having stolen it from someone else.

Elsewhere, one of Nation’s pet themes crops up again: it’s important to stand up and fight for what you believe in, rather than running away. Just as the Thals eventually accepted they needed to fight the Daleks, so here both David and Barbara challenge Susan and Jenny not to keep running away. In David’s case, this is important as it’s part of a scene that sets up Susan’s eventual departure. Uniquely, she’s just extended him the opportunity to leave with her in the TARDIS, and he’s turned it down: ‘This is my planet! I just can’t run off and see what it’s like on Venus.’ ‘I’ve never had any real identity,’ Susan replies, and Carole Ann Ford puts some genuine feeling into that reading.

Other things I noticed:

• The Black Dalek makes his first appearance, unheralded, during the battle sequence. His voice is much more shrill than the ordinary Daleks
• The Daleks haven’t yet adopted ‘exterminate’ as a catch-all catchphrase – they prefer to shout ‘Destroy!’ a lot

Next episode: The End of Tomorrow