Police have arrested two people who were planning to take a 71-year-old man, believed to have dementia, to an assisted suicide clinic in Switzerland.
The police described the man as vulnerable, and took action because they are concerned that he may lack mental capacity.
Police questioned the pair, thought to be the wife and son of the man, on suspicion of encouraging or assisting suicide.
Assisted suicide campaigners say the case highlights the need for greater clarity in the law, but pro-lifers warned that a change in legislation would put pressure on vulnerable people.
Assisting someone to kill themselves is punishable by up to 14 years in prison, though Crown Prosecution Service guidelines say a prosecution is less likely if there are compassionate motives and someone clearly wants to die.
The Police said experts will now assess whether the man has the mental capacity to make informed decisions.
The woman and man, from West Sussex, have been released on bail without charge until 8 October.
Dr Peter Saunders who is the campaign director of Care Not Killing said the case may cause some to question the current law on suicide, but he says there is no need for it to change.
He said: “The penalties it holds in reserve act as a strong deterrent to those who stand to gain from another person’s death.
“It also gives discretion to prosecutors and judges to apply mercy in genuinely hard cases.”
He added: “Any change in the law to allow assisted suicide or euthanasia would place subtle pressure on vulnerable people to end their lives, for fear of being a financial, emotional or care burden upon others.”
There has only been one previous case of a British person with dementia travelling to Switzerland for assisted suicide at a Dignitas clinic.
In May this year, it was found that an 83-year-old man was helped to make the journey to the clinic by a controversial ex GP known as “Dr Death”.
Dementia is a neurodegenerative disease but is not a terminal illness.