It has become a British rite of passage - cowering behind the sofa as a monster moves menacingly towards the Doctor who will no doubt save the day in some brilliant and mind-boggling manner.

Steve Thompson went through it when he was growing up in Welwyn Garden City in the ‘70s, watching Tom Baker flap about with his scarf, but little did he know that 40 years later he would be the one making children scurry behind the sofa.

In fact if you turned on your television a few weeks ago you would have seen the latest Doctor Who, Peter Capaldi, fighting to escape the Teller in the fifth episode of the new series, Time Heist, which was dreamt up by Steve.

"You are not just writing a monster. You are inventing an action figure," says the 47-year-old talking about the pressures of being a scriptwriter for the world famous series.

"It‘s a global brand and has been for 50 years."

Steve isn‘t on social media and never reads reviews, but has a "ritual" of watching the show with his children and says they give him all the feedback he needs. "My three-year-old watched the episode and hid behind the sofa and I felt great about that."

Steve wrote The Curse of the Black Spot and Journey to the Centre of the TARDIS during Matt Smith‘s era and says of the new Doctor: "Peter Capaldi is even better than I expected, just a phenomenal actor, and having him read my lines was amazing."

The scriptwriter had his first big break in television writing for Sherlock, after co-creator Steven Moffat saw his play Whipping It Up back in 2006 starring his friend Richard Wilson.

"He got in touch with my agent afterwards and asked to meet me, so we went for dinner and he told me about the idea for Sherlock. It was before the first series, so nobody knew what it was.

"It seemed really thrilling and the pilot looked really good and so I said yes and it filmed the following year.

"So that dinner was my career for the next seven years," laughs Steve.

The series has gone to be a global smash hit and it is not only stars Benedict Cumberbatch and Martin Freeman who have benefited.

"Obviously when you are making it you know it‘s good, but we had no idea it was going to become this phenomenon," explains Steve.

"The explosion in popularity was unreal. It was a game changer for me, absolutely. It was huge."

He has mostly stayed out of the spotlight despite the millions of fans Sherlock and Doctor Who attract, but took time out of writing a period drama for ITV to chat to me about returning to Welwyn this week to give a talk at Barn Fringe about his work.

The theatre is where the former St Albans School pupil‘s love of drama started as he first trod the boards there aged seven, later becoming a maths teacher from 1998 to 2003, before turning his hand back to drama and winning the Meyer-Whitworth Award for new writing with his first play Damages in 2004 before catching Moffat‘s eye.

He had no hesitation about saying yes to working on Sherlock as he was already a huge admirer of Sir Arthur Conan Doyle's character.

"Yes I was a fan. My parents took us on a holiday to Cumbria and the weather was terrible and the only saving grace was they were showing the old Rathbone movies on TV.

"That was the first time I saw the character, I was in my early teens and then read the books and fell in love with the character.

"That's the main thing that draws you into Sherlock, the character himself.

"Steven Moffat said to me that the main thing was that Sherlock doesn't just get involved in stories he goes on adventures and the key thing is you need to see the whole thing from Watson's point of view.

"It's a buddy show."

Steve was given free reign to create storylines and he went on to pen The Blind Banker, and The Reichenbach Fall episode in which star Benedict Cumberbatch plunges to his ‘death‘, getting the "whole nation talking".

"We hired a famous magician to come and help us," reveals the Cambridge resident, "and we sat and talked it over. Originally I wanted to chuck him off The Shard, but that would have been quite hard to film.

"So yes we knew how he survived. They sort of revealed how he did it and then pulled the plug again, but I think it will be referred to in new episodes, but I can‘t say more."

The father-of-five also says he has no idea when filming for the fourth series, due to air in early 2016, will begin or if he will be involved.

"Its a long way off so I don't even know when it will be going ahead. At the moment they are doing the Christmas special and I'm not involved in it."

He says it takes about six months to develop a 90-minute script, and there are plenty of re-writes as they try to fit the "jigsaw" together.

His biggest challenge to date was writing The Sign of Three, in which Dr Watson gets married, with best man Sherlock solving a case during his speech.

"They said it had to have John's wedding in it but apart from that they just said to have a wedding speech and I came up with the idea for encompassing The Sign of the Four.

"The brief is quite loose which is exciting. We go back and forth and talk about it but it's fun to be given that freedom to be creative.

"All I knew is that he would be the very worst best man in history because he's so dysfunctional, well a functioning sociopath as they call him, I have seen some fantastic and some disasterous speeches and been a best man once so I must remembered all the cringe-making speeches I have sat through and amplified it."

He also gets to go onto the set for filming and says of Sherlock star Benedict Cumberbatch: "He's charming. The very first time I took my kids on set to meet him on the first series he went out and bought them all sweets and they were absolutely charmed."

It was while filming Sherlock that he began pestering Steven Moffatt about working on Doctor Who.

"I must have worn him down as eventually he sent me an email saying "OK. The Tardis needs you" and I still have it, I treasure it, as he has a huge queue of people wanting to write for Doctor Who and I made it the title of the talk I do."

The first episode he wrote was The Curse of the Black Spot and he recalls being on set: "It's incredibly exciting as there's a lot of effects. It was a crazy feeling that I was responsible for it.

"Matt Smith and Hugh Bonneville were stood there with all this water drenching them and I was there in my coat and feeling guilty they are getting soaked because of me."

Talking about the difference between writing for the two shows he says: "They are very different processes. Sherlock is quite free with ideas whereas Doctor Who is a huge international brand and has been for 50 years. So there's all sorts of commercial pressures. But they have got a good script department who makes sure everything dovetails.

"There are story arches, like Clara's boyfriend, so you do get more notes for Doctor Who and have to blend more in, particularly when you have a new actor."

He watched the Ocean's Eleven films as research for his latest episode Time Heist, getting up at 8am to start work at his kitchen table, and says he has some "absolute corkers" up his sleeve if he is asked to write more.

"There's one particular episode from the '70s I would like to bring back but I'm not saying which one."

A with that mysterious teaser he is off.

Steve Thompson will give his talk OK The Tardis Needs You, at Barn Theatre, Handside Lane, Welwyn Garden City on Friday, October 3 from 8pm. Details: