London, England - The need, legality and morality of updating the UK's Trident nuclear deterrent have been questioned by the Archbishop of Canterbury.
Rowan Williams said many people would never accept the morality even of threatening destruction by "intrinsically indiscriminate" weapons.
On Monday, Tony Blair outlined plans to spend up to £20bn on a new generation of submarines for Trident missiles.
It would be "unwise and dangerous" to give up nuclear weapons, he told MPs.
BBC religious affairs correspondent Robert Piggott said Dr Williams had been frequently frustrated at being bypassed in public discussion of moral issues.
The archbishop was determined both that a national debate on Trident should take place and that the Church of England's voice should be heard.
In July, a group of bishops warned Mr Blair that the possession of Trident weapons was "evil" and "profoundly anti-God".
Church leaders have been unusually passionate and united over Trident.
The head of the Roman Catholic Church in Scotland, Cardinal Keith O'Brien, said the system prevented peace rather than protecting it.
The leader of the Anglican Church in Wales, Archbishop Barry Morgan, insisted in September that the money spent on it could instead save 16,000 children from dying from preventable diseases every day.