The High Court is to begin hearing the legal challenge of a terminally-ill man who wants the right to die.
Noel Conway, who is 67 and has motor neurone disease, wants a doctor to be allowed to prescribe a lethal dose when his health deteriorates further.
He said he wanted to say goodbye to loved ones “at the right time, not to be in a zombie-like condition suffering both physically and psychologically”.
Any doctor who helped him to die would face up to 14 years in prison.
Mr Conway, of Shrewsbury, told the BBC: “I will be quadriplegic. I could be virtually catatonic and conceivably be in a locked-in syndrome – that to me would be a living hell. That prospect is one I cannot accept.”
Mr Conway, a retired college lecturer, was once fit and active but motor neurone disease is gradually destroying all strength in his muscles.
He cannot walk and increasingly relies on a ventilator to help him breathe. As his disease progresses, he fears becoming entombed in his body.
Mr Conway is too weak to come to court from his home but his lawyers will say he wants the right to a peaceful and dignified death while he is still able to make the decision.
Mr Conway is being supported by the campaign group Dignity in Dying.
The last major challenge to the law was turned down by the Supreme Court three years ago.
It ruled that while judges could interpret the law it was up to Parliament to decide whether to change it.
In 2015 MPs rejected proposals to allow assisted dying in England and Wales, in their first vote on the issue in almost 20 years.
Supporters of the current legislation say it exists to protect the weak and vulnerable from being exploited or coerced.
The case is expected to take up to four days.