Tim Treloar said: "History is one of my passions, and particularly the history of the Second World War. Even though the Dunkirk evacuation is one of the most famous parts of the war, the rearguard - the soldiers left behind to shield the retreating British forces - is a not-often-told story. 

"It was lovely working with Nick as a co-writer. I pitched the story to him, and he said, go on then, write something. I ended up writing all six episodes, and then giving it to him. And so Nick took my script away, shaved off a lot of my waffling, and turned it into a brilliant Doctor Who story. He's added a heck of a lot to it, and it has been a rewarding experience for me."

Producer Heather Challands added: "This story spans times, places and planets! The Doctor, Sarah Jane and the Brigadier go back to World War Two in order to save Jo Grant's father from a villain hellbent on revenge! He wants to wipe out every chance of Jo Grant existing... but is there something else he wants as well? 

"As soon as Nick and Tim told me the pitch, I was hooked. It feels like it's exactly what Doctor Who should be doing: educating about real-life events and people as well as showing a human heart, with some added aliens on the side. It's epic in scale and made for a raucous and busy time in the studio – just how I like it."

Writer and star Tim Treloar said: "I'm very grateful to Nick and to Big Finish for giving me this opportunity. I think we've created something quite special together. The cast are brilliant. I was lucky to call on some people I knew who would be perfect in some of the parts. Listening to Harry Myers, who plays the evil sidekick, that voice is fantastic."

His co-star Sadie Miller added: "It's always a joy to be back and with so many familiar faces in the studio. I'm very excited that it's a huge script as well, because for Sarah, we don't often do these big six- or seven-parters. You really get to explore Sarah as a character through the big arc, and it feels much more cinematic.

"The story is so packed with different elements - sci-fi, stuff on Earth, history, and lots of really fun, very silly moments that are brilliant. But there's also a heaviness to it that I think is important - it's got a message without ramming it home too heavily."

And Katy Manning, who makes a guest appearance as Jo, said: "The Doctor and I have this wonderful, heartfelt moment together. It was lovely and a very, very great story from Tim, who of course is a great war expert, and there are some very interesting things about that in here."

Tim Treloar

Katy Manning, Sadie Miller, Tim Treloar, Jon Culshaw

Jon Culshaw, Sadie Miller and Tim Treloar

Gareth Armstrong, Tim Treloar, Jon Culshaw, Hannah Blaikie, Katy Manning, Sadie Miller, Tom Kiteley and Harry Myers

Jon Culshaw, Sadie Miller, Tim Treloar, Nigel Betts, Hannah Blaikie and Bronte Alice-Tadman

Jon Culshaw, Hannah Blaikie, Sadie Miller, Tim Treloar, Tom Kiteley, Max Bowden and William Reay