We’ve been keeping a tight lid on this story for weeks now, but RT’s Patrick Mulkern was at London’s British Film Institute on 12 January to capture a small but important moment in Doctor Who history. It was the day that director Waris Hussein met Sacha Dhawan, the actor who’ll be playing him as a young man in An Adventure in Space and Time, Mark Gatiss’s hotly anticipated 90-minute BBC drama about the early days of Doctor Who.

Hussein directed An Unearthly Child, the very first adventure in 1963, at the tender age of 24, and is delighted to be a key character in the drama. Still a working director, Hussein has helped Gatiss in his “meticulous research” and tells RT he couldn’t be happier with the choice of actor. “I am to be portrayed by my doppelganger, Sacha Dhawan, a handsome actor. Vanity prevails!” he jokes.

Manchester-born Dhawan is perhaps best known for his role as Akhtar, one of the original History Boys in Alan Bennett’s multi-award-winning play (and subsequent movie). He was at the BFI to watch An Unearthly Child for the first time – and to meet Waris and start thinking about how he’ll play the young director.

After yesterday’s casting announcement, Dhawan tweeted: “Can't wait to start this! Incredibly honoured to be part of this…” He’s actually nearly five years older than Hussein was when he masterminded Who but, as this 1960s picture of Waris shows, there’s an uncanny resemblance. “He’s taken a lot of effort to emulate how I speak,” Hussein tells RT today.

The full-cast read-through for An Adventure in Space and Time was held in central London on Tuesday afternoon, with Hussein in attendance. He tells RT: “I was very moved by it. We went round the table introducing ourselves and when it got to me there was huge applause!” He laughs and goes on to mention several other Doctor Who luminaries who also got applause – but we cannot reveal their names at this stage!

Flushed after the momentous read-through, Gatiss tweeted: “Thrilling and moving day. I’m spent!”

Filming starts imminently in London at BBC Television Centre and Wimbledon Studios. More news to follow at RadioTimes.com

(Colour photographs by Patrick Mulkern)