The need, legality and morality of updating the UK's Trident nuclear deterrent have been questioned by the Archbishop of Canterbury.
The Archbishop of Canterbury is opposed to nuclear weapons
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.
TRIDENT MISSILE SYSTEM
Missile length: 44ft (13m)
Weight: 130,000lb (58,500kg)
Diameter: 74 inches (1.9m)
Range: More than 4,600 miles (7,400km)
Power plant: Three stage solid propellant rocket
Cost: £16.8m ($29.1m) per missile
Source: Federation of American Scientists
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.
MPs to vote
In unveiling a white paper on the issue in the Commons, Mr Blair said submarine numbers may be cut from four to three, while the number of nuclear warheads could be cut by 20%.
Trident will reach the end of its scheduled life in 2024
Mr Blair said although the Cold War had ended, the UK needed nuclear weapons as no-one could be sure another nuclear threat would not emerge in the future.
Mr Blair said between £15bn and £20bn would be spent on new submarines to carry the Trident missiles.
The submarines would take 17 years to develop and build, and would last until about 2050.
He said the UK would also join the US programme to extend the life of the Trident missiles until 2042 - and would then "work with" the US on successor missiles.
MPs will vote on the plans in March after a period of debate, he said.
Conservative leader David Cameron said his party agreed with Mr Blair's position "on substance and on timing".
But Liberal Democrat leader Sir Menzies Campbell said proper consideration of all relevant factors could be made only if the decision was postponed until 2014.
Anti-nuclear pressure group, CND, said it was "very very disappointed" with Mr Blair's announcement.