Once society allows voluntary euthanasia it will have set foot on a slippery slope that will lead inevitably to non-voluntary euthanasia, the Catholic bishops of these islands have said.
In a jointly published pastoral Cherishing the Evening of Life, the bishops of Ireland, Scotland, England and Wales said "people who are dying want to know that, even though there is no prospect of recovery, they will not be abandoned.
"It is important that the kind of care a sick person receives is not dictated by the fears or the convenience of others."
The pastoral was issued to mark this year's Day For Life, which takes place tomorrow.
The bishops recalled that, in his Lenten message this year, Pope John Paul asked that people "deepen the awareness of the role that older people are called to play in society and in the church". The pope's message, they said, "was particularly forceful as it was written by an elderly man showing the world every day that all life is worth living.
"John Paul II reminded us with his own painful witness that we can never say that a person, weakened by sickness or age, is useless and is no more than a burden to society.
"We are challenged to love the life of older people with a reminder that in scripture reaching old age is a sign of God's benevolence, and longevity is prized as a special divine gift."
They said when a decision is taken to end the life of a person who is sick or elderly, on the grounds that his or her life is no longer worth living, that is euthanasia.
"The right to be able to choose to die can too easily become a duty to die. The philosophical advocates of euthanasia have often made this clear."