The inside story of how Pearl Mackie was cast as the new Doctor Who companion

So, this Council of Four (yep, we're going with this) have a decision to make. They have to choose between five – yes, five – potential stars.

"That had been whittled down," explains Pryor, who has been involved in casting every Doctor and every Doctor Who companion since the show was revived in 2005. He knows this situation better than anyone else.

"Myself and my team looked loosely at about 70 people, met about 50, and then recalled about 10. Then we brought in the final five with Peter Capaldi."

Even to get this far is an achievement. A chance to perform opposite Peter Capaldi as the Doctor in a scene written by Steven Moffat? Hell, that's about as out of it world as it gets.

But for one person, the journey is only just beginning.

"We talked it all through," says Pryor. "Everybody looked back through the auditions. We shared our views – and it was unanimous."

Congratulations Pearl Mackie! You've got the job. But how?

This is that story.

Andy, how did all this begin?

Every time we start with a part like this you’re sort of starting again. Often with Doctor Who, we’re planning for such a major part – but it hasn’t even been written yet.

Steven wrote some scenes to give us a good steer for the part of Bill, one of which ended up being only a slightly adjusted version of the clip we filmed for the announcement.

Until you have something physical on the page, it’s very hard to pin down what you’re looking for. We wanted someone who was going to be strong, funny, fresh, a new face. And that’s what we found in Pearl.

Was it always the plan to cast an unknown as the next Doctor Who companion?

For this part we definitely wanted someone new. As everybody knows, we’ve often had somebody in the show, and the showrunner has loved them so much that they've brought them back. But in this case, we wanted someone new to the show.

Where had you seen her before?

I had seen her in Curious Incident of the Dog in the Night Time, which Pearl is in at the moment. I’d seen her in a couple of Fringe plays. My assistant had seen her in several plays actually, more than I had. We were aware that she was a strong, talented young woman, and it was just a question of time before the right part came along for her.

It’s our job to see an awful lot of theatre; that’s generally where people have their best training in this country. Some weeks I'll only see one play, other weeks I can be out three nights. I have a team of two, and across the office I’d say we’re probably covering around 300 plays a year.

What made Pearl Mackie right to play Bill?

She arrived fully formed, with a strong personality and a strong sense of herself. A great deal of humour too, which is something we were looking for in this case.

We know – and I’m afraid the audience will have to wait to find out! – a little bit about her background. It wasn’t a prerequisite that she be a Londoner. It just so happened that Pearl is. I know the kind of person Bill is, and the kind of life she’s leading before she meets the Doctor – and Pearl got it.

How did Pearl react to acting opposite Peter Capaldi?

It’s that thing that’s always impossible to put your finger on: chemistry. You can’t predict that until you get them in the room together. When we did it became evident very quickly that they had a spark that was new and exciting and fresh. Peter responded incredibly well to Pearl in her audition. It was like they were feeding off each other, swapping ideas of how they might play the scene. That’s always exciting; it’s full of possibility.

How important was that in terms of the final decision?

I would find it hard to cast a companion without having them in to read with the incumbent Doctor. It’s all about that relationship. They are going to spend months together on and off screen.

Peter did have opinions in recalls, quite rightly, but he also knows you’ve got to look at the long game with it and find somebody who is going to be able to develop across series. He’s always very happy to listen to Steven’s views, my views, Brian Minchin’s views. We very much made the decision with Peter in the room.

You were also responsible for casting BBC1's Undercover, which has been praised for its 'colour-blind' casting. Was that also part of your thinking with Pearl?

I’m quite proud of Doctor Who’s record on this in recent years. It’s television’s job to reflect the world that we live in, and if you can’t do that on a show like Doctor Who, then where can you?

There’s been a lot of discussion about diversity lately, for good reason. It’s a complicated subject, but in the end it’s about anyone growing up and feeling they can have a career in acting, behind the camera or involved in the arts.

Unless you see people like you, it’s quite hard to imagine that it’s a profession that you can go into. The more we can reflect the demographics of the country, the more people will say, ‘Yes I can have a career in that. It’s not just something for a certain type of person.’

There are so many stories to be told and we should be telling everyone’s stories. It is a conscious thing with me to be aware of diversity on everything that I work on.

Pearl was little-known before this announcement. Do you feel responsible for her, making sure she can handle the attention?

Yes I do. It is quite an unusual challenge. Big TV shows these days, there are a lot of associated activities: the tours, the conventions, the additional material. You need them to have their heads screwed on.

We have a duty of care to people, not to throw them into the madness before they’re ready for it.

How long has Pearl known she was the new Doctor Who companion?

We’re talking a matter of weeks. These days it’s very difficult to keep things under wraps. Initially there were only maybe nine or ten people who knew, but as time goes on, that number has to grow because of costume, shooting the special trailer, all the logistical and practical things that surround filming.

The longer time goes on, the more people know, the harder it is to keep a secret. Charlotte Moore [controller of BBC TV and iPlayer] had this great idea of putting it out in the middle of the FA Cup semi-final, because that happened to be the nearest date to when there was a big national event that would get a bit of focus.

As is customary, I called Pearl's agent with the news, so that she could tell her. Once the news had sunk in, we all caught up with Pearl by phone, text and in person.

How different is it casting for Doctor Who compared to other dramas?

I think when you’re announcing a Doctor or a companion then you do feel the spotlight. These decisions are quite public; there’s an appetite for the news. Whereas most other dramas I work on, people aren’t particularly aware of what’s coming, and there’s little interest before the show comes out.

The thing I love about working on the show, and the reason I’ve stayed with it for so long (apart from the fact that they keep asking me back!), is it’s always so different. Every episode is different.

You don’t know whether you’re going to be casting a historical drama or a space episode, a sci-fi episode, a contemporary British episode, an American episode. Whereas most shows, however well they’re written, you’re still casting a policeman, a nurse, a villain… As great as that is, you’re operating in the same world all the time. With Doctor Who, I never know where I’m going to end up next.

Which is harder, finding the next Doctor or the next companion?

I would say the Doctor. A companion can be anything that a writer wants them to be. But with the Doctor, you’re looking for a particular kind of leading man, a particular kind of leading actor who has to have that innate "Doctor-ness" to them.

I've worked on the show for so long now and I could try write down a list of adjectives, but it would be different for every Doctor. But there is always a slight otherness about them. There has to be that real sense of comedy, but also a lot of deep emotion and heart in the performance.

It requires actors who can turn on a penny. It’s never going to be an easy job to pull off – and not everybody can do it.

What was your bravest casting decision on Doctor Who?

I do get asked this a lot and I change my mind quite frequently. But right back at the beginning, casting Christopher Eccleston and Billie Piper together has to be up there. A lot of people thought we were quite mad, but there was something about it that just felt right. Billy did an amazing audition, and it was quite exciting to have the public wondering how it was going to work, when we already knew that it would.

And was Peter the easiest, given how much of a fan he is?

I didn’t know quite how much of a fan Peter was before we approached him. I knew he was a fan, but not that it ran so deeply.

It is funny: when Matt Smith left, we didn’t have a policy of where we wanted to go particularly. We just threw the ideas around and Peter kept coming up again and again. It just felt like the right thing to do.

Doctor Who runs in cycles. You have a new companion, and sooner or later a new Doctor arrives too. Have you discussed those plans yet?

No, I quite deliberately don’t ask until the time is right. I’m very much focussed on the show at the moment. Pearl hasn’t even started filming, and I honestly don’t know what’s going to happen beyond this series yet.

What about new showrunner Chris Chibnall? Have you spoken with him yet?

I haven’t yet. I’m thrilled about Chris, I’ve worked with him a lot on Torchwood and Doctor Who. I think he’s the perfect choice, but he’s very busy on Broadchurch now, and will be for the foreseeable. I haven’t had any conversations beyond this series.

And finally, what are you most looking forward to seeing from Pearl Mackie as Bill?

I’m looking forward to seeing that playfulness that you saw in the clip. How that humour and warmth will play out. I think already it's clear she’s her own person who’s not going to be impressed easily. I think that’s quite a fun thing to explore, and it’s something that Pearl is brilliantly equipped to do.