For Craig, my husband, allowing the cameras to film his last moments in Zurich was about facing the end of life honestly. This wasn't a film about him personally. He was keen to have it shown because when death is hidden and private, people don't face their fears about it. They don't acknowledge that it is going to happen, they don't reflect on it, they don't want to face it. That's the taboo.

Craig had his first random symptom of motor neurone disease at Christmas 2005. In the spring, he deteriorated very quickly. He lost the use of his arms and, during the summer, he was on a ventilator 24 hours a day, then he was starting to lose rapidly the use of his legs. He wanted to remove a veil so that people could see how comfortably someone could die who – without this option of assisted suicide – maybe would have had a very painful death. Craig had been a teacher, and you could say he made this film with his educative hat on. Both of us had been interested in why society and laws regulate very specific decisions that we make. He had resisted the Vietnam War. If he had had to leave the US to avoid the draft, he would have – but he was lucky, it didn't come to that. And I have had an ongoing interest in the regulation of the body, and how the law regulates the body, so this was something that we were interested in before Craig's illness.

We met when we were at college in the Chicago area. I came to Britain to study in 2001. A couple of years before that, he had retired from his 20-year career in IT and he had taken up some teaching posts, so I continued my studies, and he found a teaching post in Harrogate, north Yorkshire, teaching maths and science.

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In late March or early April, he was having a lot of trouble breathing. The onset of motor neurone disease (MND) symptoms can be quite different for different people, and for him it was his breathing. He was diagnosed by the end of April by one neurologist. He got a second opinion, and then he was sent to a specialist consultant who said, by a process of elimination, that that was what it was. By early June 2006, he knew he had MND.

This disease was, in an odd way, his real nightmare because he had a real fear of paralysis and of suffocation. I knew that about him. I had known about that fear for years.

Since meeting Craig when we were in our early 20s, he had always been very clear what he would do if he was in a situation like this.

In fact, in the film my daughter says that she remembered from childhood her daddy saying that if he ever had a fatal disease and he felt he needed to go quickly, he wanted the kids to take him to Amsterdam for a night of fun and then he wanted to end his life the next day.

So, in his mind he always had this travelling to Amsterdam sort of thing going on, but when he investigated it he found that it was not possible because he was not a Dutch citizen.

Given those two facts that I had known about him for decades, it was not at all a shock to me when he had to contact Dignitas. He would have waited longer had he had a prescription sitting by his bedside that he could use when he needed to but, because we are not at that point yet, he had to make the decision sooner than he would have liked.

After Craig set his appointment with Dignitas, they asked him if he might be interested in speaking to John Zaritsky, who had been in contact with Dignitas for about a year.

"They said, 'We have this person that has a real interest in this subject. We feel okay about him and he is looking for someone to film at the end. Are you okay about it?' And Craig said yes. John travelled to Harrogate and he interviewed Craig four or five days before he travelled to Switzerland.

When I first saw John Zaritsky's film, it was what I expected it would be, and what I think Craig would have hoped it would be. I was very happy with it. I have been to screenings in Amsterdam, Toronto and Vancouver, and I have taken questions from the audience. The most negative reaction I have had was from one person when it was shown one time in the US at a film festival.

Most of the time, older people are very understanding. Younger people will say things like, "the medical profession could have taken care of him", but I think that is just youth and inexperience talking.

When you look at the fine points of MND, most people might die peacefully – but Craig's fear was of being one of the ones who wasn't in the "most" category, and that he would get to the point where he couldn't do anything about it. That horrified him.

* The programme is to be broadcast at 9pm on Sky Real Lives.