Alex Kingston said: “We have gone post-Library! We’ve done another episode in the past where I was within the database, which I loved, and I thought that’s the only way you could go forward with River, given her situation. So, I was actually really surprised when this box set came my way, and that we are now so far advanced in the history of Earth that she is able to be brought out as data and put into a cloned body. So very, very clever!”

Producer David Richardson said: “Robert Valentine has done something remarkable with this four-hour drama, which tells the story of the last days of planet Earth before it is destroyed by solar flares, a story told from the perspective of a woman temporarily brought back from the dead. It’s heart-breaking and exciting and doom-laden and, perhaps when you least expect it, uplifting and inspiring.

“When every single day during the recording, your leading actress says “This script is brilliant”, you know you’re onto a good thing. Even better, at the end of the last day, Alex popped the script in her bag and announced that she loved Last Words so much she was taking it home to keep and treasure.”

Writer Robert Valentine added: “Originally, I thought I was going to be writing the final ever River Song story. Quickly I realised that I wasn’t, but I thought it would be fun to write something that feels like it’s the last we’ll ever see of River, and actually give that problem to her. Her life is usually intertwined with the Doctor’s, so I thought, what is her life like after her great relationship is over?

“And, the brief was to do a prequel to The Ark in Space, which is a Doctor Who classic, at the same time. When I went back and rewatched it, I realised that I wouldn't be allowed on this ship, I would have been one of the ones left behind. So I thought, let's give River a mission that leads into The Ark in Space, but with sympathy for those people who aren't on the Ark.”