‘Now, they’ve all gone. None of them ever understood.’ This dramatization of the origins of Doctor Who smooths some of the rough edges (Hartnell’s attested racism, homophobia and antisemitism), and conflates a few events, but the end result is a remarkable, moving tribute to the pioneers whose make-do-and-mend approach created a legend.

The show is presented as a scrappy underdog, made in unsuitable studios by an upstart ITV man, a Jewish woman and a gay Asian fighting to get the programme made in the face of BBC indifference and bad luck. Newman arrives at Television Centre like one of the BEMs he abhors, stream-rollering through uptight car park attendants and tweedy incomprehension. Lambert has to prove her credentials to condescending men. Even Hartnell, their star, has something to prove – a chip on his shoulder because he never received the success he expected after Brighton Rock, as a legitimate character actor.

For old fans, there’s a joy in seeing scenes from 1960s classics (including the lost Marco Polo and The Massacre, and a hint of Doctor Who in an Exciting Adventure with the Daleks) recreated in colour, as Menoptra and Robomen flit across the screen. It’s fun, too, to spot Hartnell era actors (Russell, Ford, Wills, Marsh, Eden) in among current stars like David Bradley, Brian Cox and Lesley Manville. For newer fans, Gatiss peppers the story with some recognisable touchstones like ‘I don’t wanna go’ and Matt Smith.

Mostly, this is the story of William Hartnell – a bitter man whose relationship with his own granddaughter improves as he becomes a beloved children’s TV star, seizing this winter-time career opportunity with both hands only for it to begin to slip away as his health fails him. As the underdogs become successful TV directors or producers, and his co-stars move on to other work, he becomes the show’s one constant, increasingly isolated as each press call heralds new cast changes. By the end, he’s a proprietorial tyrant, the master of his small kingdom – a fate that also befell Tom Baker and (to some extent) Jon Pertwee – clinging to the mantra ‘You can’t have Doctor Who without Dr Who.’ Like them, his hands have to be prised from the TARDIS console. It’s a wonderful performance from David Bradley, and very fitting that he’s now become a legitimate first Doctor in his own right.

There are some flaws – Hartnell’s is the main story, but more time is devoted to Lambert’s challenges as the first woman in the BBC, so it’s odd when she vanishes towards the end. If this were a movie biopic, it would have introduced us to her, Hussein, Newman and the rest through Hartnell’s eyes – which might have been very effective, as surely his attitude to them would be every bit as fusty as Rex Tucker’s.

But I watched this, as broadcast, with friends the night before we went to the 50^th anniversary convention at the ExCel in London, on one of the happiest weekends of my life. It’s as precious to me as The Five Doctors – and how fitting it ends with the same clip of Hartnell that opened the 20^th anniversary special.

Next Time: The Day of the Doctor