TV special Blackadder: The Lost Pilot sees Sir Tony Robinson on a quest to discover the truth behind the Blackadder origin story. Tony's journey takes him back in time to find out where Blackadder really began, and to uncover the story of the never-before-broadcast Blackadder pilot episode.

It's a personal story for Tony - Baldrick has defined his career and playing the character transformed his life. But Tony didn't play Baldrick in the pilot. And there's so much about Blackadder's beginnings he doesn't know. Along the way he speaks to comedy greats including the series creator and writer Richard Curtis and co-writer Ben Elton. The climax of the programme is a special screening of the never-before-broadcast pilot.

What's it been like returning to Blackadder's origins?

One of the interesting things about making the documentary is how every one of my interviews with the team behind the pilot was like a school reunion. We all immediately picked up the relationship we had 40 years ago, rather than having to start afresh. That was very, very strange.

What was evident from the interviews is there's an awful lot of goodwill towards the pilot. Even though it was very experimental, and it's not what Blackadder became, you can see how the scaffolding in the pilot built the future series.

How did you become Blackadder's historian in this documentary?

The first question I was asked was a theoretical one. The production knew the rights to the pilot existed but obtaining the rights after 40 years was a nightmare, so they asked if I would be interested in being involved if they were able to get the rights. I replied I'd love to be involved.

There's so much I don't know about Blackadder. I talk about the show to the press so often and I've been involved in two documentaries, but I was just a hired turn who turned up for six weeks every two years for filming. All the politics behind the scenes, everything that was taking place behind the cameras, and how the decisions that were made came to be made, were aspects I didn't know much about at all. I loved the idea of finding out more.

What I didn't realise was, by saying all that, I was pitching to be the presenter of the show. They said to me, "Why don't you present the documentary if you really don't know that much and you're hungry to learn? Why don't we just let you off your leash?" I was really pleased to be asked.

I do have a sense of ownership about the series, because there are very few comic performers who are given a character who becomes a national icon. I'm desperately proud of that, and to be able to recap how that character was brought to life is very important to me and my heart.

Had you ever seen the pilot before making this documentary?

I'm like everybody else involved in this film - I must have seen the pilot, but it was 40 years ago and I can't remember.

What everyone said is they cannot remember for the life of them if they've seen the pilot. Some people said they didn't even know there was a pilot and then when they watched it they said, "Of course! I remember that!". That's exactly how it was for me - the memory had completely faded away, but as soon as you see it again, the memory becomes very vivid. I was enormously excited to watch the pilot.

Which of the show's creatives do you meet during the documentary?

I've spoken with Ben Elton, Richard Curtis, John Lloyd, the producer, and Howard Goodall, the composer. To catch up with them was lovely, especially as it made me realise there is still so much friendship after all this time. We've all gone on to do different things, which must have felt to all of us to be equally important, yet everyone had a special place for Blackadder in their hearts. We all agreed it doesn't feel like 40 years since the pilot.

How challenging has it been to gather these distant recollections?

Imagine if you and your family all gathered together today and shared memories about a summer holiday 40 years ago. What you'd find is that everyone would tell a different story and, for a start, they'd probably be the star of it. Everyone would remember different details and in different ways. Some of the time you'd disagree with their version of events.

That's how it was with Blackadder; it was like trying to put a jigsaw puzzle together, except you've got three lots of pieces from three different jigsaw puzzles which all share the same subject. John Lloyd, the producer, remembered it in a totally different way as to how I remembered it. I don't think I was quite as important to his memories as I felt I should have been.

Could any of you have predicted Blackadder would still be held in such reverence and affection 40 years on?

There are very few series which continue to be held in such affection by so many people as Blackadder. I think we're all slightly puzzled by that. We can see reasons why that might be the case, but we don't actually know if they are the reasons.

You can say it hasn't dated in the same way as other shows because it's historical, but there are other historical series which haven't stood the test of time.

Perhaps it was because of the talent of the people involved, which is true, but we've all done other things which have bombed.

Maybe its longevity is because there were so many people involved in its creation the show was rigorously scrutinised in a way one normally wouldn't be, due to the enormous time pressure of making television comedy. There is a lot of truth in that.

What we can say Blackadder did do is capture the talents of an awful lot of very bright and talented people at exactly the right time in their lives.

Do you learn how Baldrick came to be Baldrick during the documentary?

We talked about him quite a lot, because he had a different number of brain cells in each series, usually less than in the series before. Again, memories of his change differ, which is because Blackadder was always a very collective enterprise. You had Ben [Elton] and Richard [Curtis], who were driving the writing, but nevertheless, all of us contributed little grace notes to the writing and it was shot in a variety of ways.

How did his stupidity change over the course of the series?

In the first series, I think he was much brighter than in the pilot. Then in the second series, he became as stupid as he was in the pilot, in the third series he was even more stupid, and by the fourth series he was brain dead.

It was completely arbitrary and loads of people had turned it down. I was living in Bristol and, four days before they were due to make the pilot, there was a thump from the front door. There, by the door, was a script from the BBC. I phoned up my agent and asked, "What's this?" She replied, "I was meaning to tell you about that. They want you to play this little part in Rowan Atkinson's new series." I browsed my way through the script and the part was so small I couldn't even find it the first time.

All my life I had wanted to be involved in what I thought of as Oxbridge comedy, from That Was The Week That Was onwards. I kind of couldn't believe they had been able to make all these wonderful series without having met me, because they were so clearly written with my sensitivity in mind. It's like that feeling you have when you hear a piece of music which speaks directly to you.

So I had the excitement of being able to play this part and then the disappointment of not filming the pilot, due to a strike at the BBC. I hung around but nothing happened, and I then landed a very nice job at the National Theatre. Then the team contacted me to say the pilot was going ahead, but my job meant I wasn't available for filming.

I thought the moment had passed, so when I later had a call offering me the role, I thought they were taking the piss. They rang me up and said, "By the way, we've got a series of Blackadder." I said, "That's great! Enormous congratulations and give Rowan my love. I'm so pleased for you." They replied, "It's good for you, too." I asked them what they meant and they replied, "We want you to play Baldrick."

The chemistry in rehearsals must have been unforgettable...

I had a wonderful time during that first week, the week that ended with the pilot not happening. In that rehearsal room I just felt absolutely at home. I felt like I'd found my brothers.

How much have you enjoyed the juxtaposition of playing Baldrick in a new Comic Relief sketch and this documentary exploring his dim and distant past?

What was extraordinary about the Comic Relief sketch was how the quality of Richard's writing meant I slipped back into the role, like you would slip into your favourite pair of slippers.

The reaction was so charming. I had a wonderful week leading up to the sketch and then a couple of wonderful days afterwards, because the press were charming, the public were so supportive, and we raised a lot of money for important charities. I said to my wife that everybody once in their lives ought to have the experience I had in those few days on the National Health Service, because it's so good for your soul.