|Archbishop of Canterbury Rowan Williams|
Dr Rowan Williams drew parallels between the change in attitudes in society towards abortion since its legalisation and the impact of a change in the law to permit assisted suicide.
"The default position on abortion has shifted quite clearly over the past 40 years - and to see the default position shift on the sanctity of life would be a disaster," he said.
"We are not committed to the notion - the eccentric notion - that Christians believe we should cling to life at all costs.
"We are committed as Christians to the belief that every life in every imaginable situation is infinitely precious in the sight of God.
"To say that there are certain conditions in which life is legally declared to be not worth living is a major shift in the moral and spiritual atmosphere in which we live.
"We can be realistic, we can be compassionate, in the application of the existing law."
Dr Williams was speaking during a debate at the General Synod of the Church of England on the independent Commission on Assisted Dying headed by former lord chancellor Lord Falconer.
The report published last month called for a change in the law to allow doctors to be given the right to help some terminally ill people to die.