Series producer David Richardson said: “I feel privileged to have produced this very special episode, and the recording session was very special too.

“To have all of these wonderfully rich characters together was a treat, and to have David Tennant and Michelle Gomez going head-to-head was joyous. Michelle loves to play with the script, and she improvised beautifully - and David took her improvisations and matched her.

“During the recording I wondered how much might make it to the edit, but it’s all there within the final scenes. Joyous - I’ve used the word again. I’ve no other way to describe it.”

Writer Jonathan Barnes said: “I always try to include a personal element in my stories so I was pleased to be able to write a sort of love letter to the work of HG Wells as well as the required ingredients.

“It’s a commentary on fandom too in some ways. The Doctor lands on a planet which seems to have been remodelled as an exact replica of the fictional London in Wells’s War of the Worlds... but who could be responsible for such devilry? Well, check out the front cover! Hopefully there are a few a surprises along the way too...”