"she opened her mouth wide and howled - a sound which made the hairs stand up on the back of your neck."

There are those who will wonder why a woman with chronic asthma smoked like a chimney.

But they'll be the people who aren't in the terminal stages of motor neurone disease. In other words, most of us.

The following is from a transcript of a conversation between Diane and her husband Brian which we filmed for Panorama. A typical exchange.

Diane: "Ahhh"
Brian: "Itch? Where? Nose?"
Diane: "Ahh"
Brian: Middle? Tip? Do the whole lot, get it all over and done with?"
Diane: "Ahhh"
Brian: Is that it? Have I got it?"
Diane: "Ahhh"
Brian: "Oh, right down. Is that better?"
Diane: "Mmn"

If no-one could understand what Diane was trying to say, the grunt became a low-pitched scream.

Diane was totally reliant on her husband, Brian

If you still couldn't understand, it would start to get louder. And louder, until she opened her mouth wide and howled - a sound which made the hairs stand up on the back of your neck.

You could hear this cry from halfway down her street. If you didn't know that Diane Pretty lived in that house, you'd think it was an animal being tortured.

It wasn't. It was a 43-year-old mother of two who wanted someone to help her die. I heard this cry in its various guises many times over the month we were filming with Diane and Brian.

Although it began to shock me less as time went by, it never ceased to make me think that before we make up our minds about voluntary euthanasia or make sweeping judgements about other people's quality of life, we should listen to a cry like Diane's and attempt to understand what she meant when she said that for her, life was worse than death.