Dr Harris says desperate people often ended up botching suicide attempts
The law should be changed to make it easier for terminally ill people to die, Oxford MP Evan Harris has claimed.
He said more than 900 British people a year were forced to get illegal help to die and the consequences for them and their families could be severe.
But Labour's Andrew Smith, MP for Oxford East, argued that most doctors did not want to see the law changed.
Justice Minister Maria Eagle said it was a "difficult" issue and one the government would continue to consider.
In a short debate at Westminster Hall, Dr Harris, a qualified hospital doctor, argued that 16 British citizens a year travelled to Dignitas, the Swiss clinic that helps people with chronic diseases to end their lives.
"The Home Office has identified about four cases of so-called mercy killings each year which is probably only a small fraction of the real number of such cases, which often never reach the courts," he said.
"Each year a number of people resort in desperation to violent and often botched suicides.
"A number of people find they have to refuse food and water in order to exercise control about their time and manner of death."
The Lib Dems' Oxford West and Abingdon MP said assisted dying was already taking place and it would "be better to put this on a legal footing with whatever safeguards" Parliament thought appropriate.
But Mr Smith said: "Do you not accept, as I think most of the public do, that there is an important difference between not intervening artificially to prolong life and actually intervening to shorten it?"
Dr Harris said he agreed there was a difference but it was not so great as to justify such variations in treatment.
Ms Eagle concluded: "It is very difficult to be clear precisely what the law should be if one accepts it should change and what the safeguards should be."