During the final shoot for the new series, Russell T Davies sees a familiar face...

Closing down.

Season’s end. The final hour.

It’s been a mad old shoot, busy and nuts and hilarious and wonderful. But now it’s time to pause. The lights go out over all six studios, chunk, chunk, chunk, that great big noise that stage lights make on film when they’re turned off. (Do they really make that noise? I always ask for it, on TV, I sit in the final mix and if a light goes out, I say “Make it go chunk!” “It’s a bedside lamp.” “Chunk!”)

The lights are still burning on just one set. The TARDIS.

And there’s Ncuti and Millie, acting their hearts out. It’s not the last scene of the episode - I don’t think I’ve ever shot a last scene last, or a first scene first. This one’s a middle bit of the finale. But exciting! Everything is at stake! Enemies are being fought! Fight, Doctor, Ruby, fight!

I stand at the back of the studio. Millie catches my eye. We wave across the distance, but I don’t step in. They’re busy. Clock ticking. But around me, people are drawing in. Crew, office staff, actors. It’s been a week of goodbyes - Yasmin Finney wrapped a few days ago, big hugs, see you soon - but it all comes down to this. The last scene. It’s kind of a tradition, to go on set for the closing moments. Not a cast-iron tradition, cos sometimes the last scene is in a field at 2.00am, but if you can, it’s nice to come and acknowledge the moment. Plus, there’s a party tonight, that helps! So there are dozens and dozens of people, standing in the shadows off-set, bathed in the glow of the monitors. One more take. Jamie the director tells Ncuti to slide to the floor a little slower, or maybe faster, I’m too far away to hear.

And there, to my right, Bonnie Langford! The Doctor’s faithful companion, Mel, come to say goodbye (did I say, there’s a party?). A hug. Some days I call her Bonnie, some days I call her Bonita, today I say, “Hello Bonsai.” “Oh, I’m Bonsai, am I?” “Yes, like a tiny, beautiful shrub.”

Then we hush, and watch the action - one more take, okay - and I look at Bonnie, and I think how funny this is. To be standing here with her. I consider the whole thing. Life. Careers. Choices. And in whispers, I tell her a story I’ve never told before.

Many years ago, I was cast as a Play School presenter. It didn’t last, I recorded one episode, felt profoundly that I was on the wrong side of the cameras, and walked out of Television Centre saying “No thanks!” I chose to go back on the dole. God, you’re cocky when you’re young. But when I recorded my one and only episode, we rehearsed in the old North Acton rehearsal rooms. Famous, to a Doctor Who fan, as the site of rehearsals for our favourite show. I thought, I wonder…?

So Play School had a lunch break, and I went to the canteen, and sat down with my food, and…

There they were. Doctor Who. I was in the same room as Doctor Who. Oh my God. I could see them. Over there. Sylvester McCoy and Bonnie Langford - all smiles and energy - and a lot of young actors, all laughing and hooting and chatting. A bright bunch of fun. Even from a distance, I could tell; that’s fun over there.

I didn’t know then, that this was a rehearsal for Paradise Towers, and the young actors were Red and Blue Kangs. I only thought, that’s Doctor Who. That’s actual, real, genuine Doctor Who being made over there, and I’m over here. I’m in the wrong place. Oh, how I wished. How I wished with all my heart that I could be on that side of the canteen.

Then I went back to work on my one-and-only episode, and I tucked that moment away as a memory. A once in a lifetime thing.

But here I am now. With Bonnie. On the TARDIS. And… that’s a wrap!

Whoops, claps, cheers, hugs, hooray! Lots of noise, and Phil Collinson makes a lovely speech, but really, I am smiling and thinking: 36 years. It took me 36 years to be on this set with Bonnie Langford as Mel, making brand new Doctor Who.

Go on. Make a wish.