"Basically I was a horrible child and I really liked nothing better than finding out unwholesome facts and writing scary stories," he confides. "I knew I wanted to write gory stories and at that time I thought I would have to make my living writing stories about history and English as they seemed to be the subjects which had the most gore in them. But then I realised that actually science has lots of stories in it – and that they can be really horrible!"
"It was actually a lucky break or a well-placed letter – whichever you want to believe," he says. "Because I wrote this really cheeky letter to the publishers Scholastic saying that if they were looking for someone to write a horrible science book I was the one.
"And would you believe they actually let me write a science book and put lots of horrible bits in it – and then it was hugely successful."
"I can't actually tell you how many books I have written now," he says. "It is definitely more than 30 but the thing is that we are constantly bringing out new editions or updating things because science changes all the time. So there are probably about 60 different editions in all.
"But I can't see that I will ever run out of subjects because I am constantly coming up with ideas. Science is really about being alive – and until such time as this life is suspended those ideas will keep coming.
"There are lots more books I want to write. I would like to do another one looking at human evolution, then robots as they are really interesting, then space because so much is changing so quickly there. I would also like to write about atoms because that field is moving so fast and children will really need to know more about it.
"My approach to a subject is to vastly over-research it. I have become quite good at science by writing these books so have got quite a lot of knowledge already but then I really like finding out more information. If I over-research then I don't just have all the facts I need, I have a lot more – and that means I can really choose what I want to include.
"The thing about a Horrible Science book is that actually it is all about imagination. The more you know the more you want to know and the more you want to develop that."
Which is one of the reasons that Nick believes the stage show has been so popular. Created by Birmingham Stage Company, who have also adapted a series of Horrible Histories theatre productions, it tells the story of Billy Miller who enters the mad theme park world of Horrible Science. With time against him, Billy has to battle lots of hideous facts and factors to ensure life can go on.
"First of all the stage show is about entertainment," says Nick.
"It is like going to the cinema only better. Who doesn't like watching a good film? And when that film is live and has got lots of great bits in that is an added bonus.
"On top of that it uses 3D and I can put my hand on my heart and say it is much better 3D than you see in the cinema. Some of the effects are mind-boggling. When I saw it there were children and adults who were clearly enjoying it.
"And finally it is education. Parents can take their children knowing they will enjoy it and learn something – and I mean the parents as well as the children!
"What is really clever about the production is that it is actually a story on a very fundamental level. It was written by people who really understand how a play works and they made sure the script wasn't too technical so it wouldn't go out of date and doesn't need constant updates."
"I know that teachers read them because they tell me," he says.
"They want to know what their students are reading! And the books have helped many teachers because they have helped people to realise that science is exciting. And that it is full of things which will really fire the imagination.
"Children love things that are horrible – it interests them. The aim of these books has never been to make children sick or give them nightmares. What I want is for a child to go 'yuk' and to be so interested in what has made them go 'yuk' that they want to go out and tell their friends and their parents about it.
"And what we have done from the start is try to make them accessible for children of all reading levels. Every child is different and while some will want to read the book cover to cover, for others there are other ways in. So it may be that a child who has not developed so much as a reader may start by looking at the cartoons or having a go at some of the experiments. And then hopefully that will draw them in to read a bit and then a bit more.
"It is brilliant if a book like that can really fire a child's imagination so they want to read it and then go on to read more."
The books have also opened up new avenues for Nick. One of his latest ventures has been the design of the Horrible Science of Submarines Exhibition at the Royal Navy Submarine Museum at Gosport near Portsmouth.
"I did that together with Tony de Saulles, who illustrates Horrible Science," he says. "We really enjoyed it and it was a really rewarding experience to go to the exhibition and see how much our hard work had paid off and how popular it was. It was a bit like the stage show really in that it needed to appeal to children and adults. You know that it will be parents who are taking their children to these exhibitions and they need to be interested too. You can't just appeal to the children."
With Horrible Science now global, Nick has developed a new hobby – looking for his books all over the world.
"It's not just airports where I look for the books," he admits. "It is really good to see them in shops wherever you go. I have always been interested in book shops abroad but now I can look for Horrible Science books as well!
"Horrible Science has been translated into 40 different languages and is a worldwide phenomenon. It is a best-selling series in South Korea. And I have just written a new book all about climate change just for China.
"It is great that something good which is produced in Britain has been so successful in so many other places. It means people all over the world can enjoy Horrible Science. So if the books can travel, then why not the show? It would be great to see the stage show become a worldwide phenomenon too. Who knows – next step Broadway?"