I think he was long overdue a biography. March 2018 will be the centenary of his birth and it is time for his full life story to be told. It has been 45 years since his death and it is important to have got on record the views of his contemporaries. What attracted me at first was the brilliance of his performance as the Master, then as I saw more and more of his early career it was the breath-taking range of his acting, and then when talking to people who knew him, it was the warmth and attractiveness of his personality.

I’ve been able to access a wealth of previously unseen records which shed a lot of light on Delgado’s life before Doctor Who. From the Ministry of Defence I obtained his complete war record (the legendary and very detailed form B199A), the school he attended is still going strong and gave me materials from the 1930s about his education, the London School of Economics provided me with his student file. While we might know a lot about Doctor Who, there were decades before then that I had to reconstruct from paper trails in archives all over the place.

I was privileged to speak to many people who knew Delgado and very quickly a theme emerged: there is just not a single bad word to say about him. But what struck me was that no one was talking about him using platitudes, it was just over 40 years later people still have such vivid memories of him as the most charming, intelligent and decent man they knew.

On working with David Bradley

David’s absolutely fantastic; I’ve always admired David as an actor. He’s extraordinarily powerful and skilled. He’s been around for so long and really knows what he’s doing but that’s great. The way that he’s sort of created this version of the first Doctor is incredible because he really looks like him but he also acts like him, he acts like William Hartnell.

On working with Steven Moffat

He’s one of the wittiest, funniest people that I’ve ever met. I think Steven could have easily been a stand-up comedian in another life. One of the most entertaining things I will always remember about Doctor Who is at the start of each season, he asks me around to his house and he will tell me what’s going to happen to the Doctor and he will go through all twelve episodes, just himself in his kitchen describing it all and it’s absolutely hilarious. It’s doubly hilarious as you go on because obviously some of the episodes don’t turn out quite as well as he’s described them, or don’t have quite as much money and are a little less focused. But he’s just a brilliant, brilliant writer. Just today we’re doing a scene which is close to the end… we’re all very concerned about how the twelfth Doctor leaves us so we’re hypersensitive about trying to make it the best we possibly can. I had expressed a little discomfort about one of the scenes leading towards the end and he re-wrote it, he re-wrote completely and quite brilliantly overnight which is fantastic; the down side is I have to learn it.

On why he decided to leave leaving Doctor Who

I realised that there’s only so much you can do and keep it fresh. I’ve never really been in a long running television series…. I’ve never been in something where you work every day for nine months of the year filming and I’ve loved it but I sort of thought if I do another year I might just start getting used to everything and that’s not the way I’ve been. I’ve always been somebody who wanted to have artistic challenges, enjoy myself and do new things.

When asked by Jo if he feels blessed for being a part of Doctor Who

I can’t even begin to tell you. Blessed isn’t a big enough word. It’s extraordinary, I keep saying privileged isn’t even a big enough word. It’s just a magical thing, to have had this time it’s just been amazing and extraordinary because there are only twelve of us so far who have been in this position. But it is a place where you see such kindness and you see such love and you see how good people are and also you can enter people’s lives in a very very positive way and you see great things. That will never happen again, there isn’t another part where that can happen and so that has been an extraordinarily privileged place to be.

His advice to the next Doctor

Strap yourself in because it’s a rollercoaster but enjoy every second because it’s brilliant.