The last moments of a terminally ill British man who travelled to a Swiss suicide clinic will be shown in a documentary presented by the author and euthanasia campaigner Sir Terry Pratchett.

The writer, who was diagnosed with a form of Alzheimer's disease in 2008, is shown at the Dignitas clinic in Switzerland with the 71-year-old motor neurone disease sufferer named only as Peter.

Pratchett, best known for his international bestselling Discworld series, said he was "a firm believer in assisted death".

He said: "I believe everybody possessed of a debilitating and incurable disease should be allowed to pick the hour of their death. And I wanted to know more about Dignitas in case I ever wanted to go there myself."

In the hour-long film, which will be broadcast on BBC2 in the summer, Pratchett compares how different European countries deal with the issue and meets people who want to control how and when they die.

It is not the first time assisted suicide has been shown on television. In 2008, a documentary on Sky called Right To Die? showed 59-year-old Craig Ewert, who also suffered from motor neurone disease, end his life.

The disease causes muscles to waste, leading to loss of mobility and difficulties with speech, swallowing and breathing.

The BBC's commissioning editor for documentaries, Charlotte Moore, said: "Assisted death is an important topic of debate in the UK, and this is a chance for the BBC2 audience to follow Sir Terry as he wrestles with the difficult issues that many across Britain are also faced with. I hope this sparks a constructive debate that people across the spectrum of opinion can engage in."

Dignitas was founded in 1998 and takes advantage of Switzerland's liberal laws on assisted suicide which suggest a person can be prosecuted only if they are acting out of self-interest.

More than 100 UK citizens have so far gone abroad to die in Dignitas clinics, where nearly 800 people from the UK have become members – the first step for those considering assisted suicide.