It is in the UK’s national interest to keep the Trident nuclear weapons system, a group of former ministers, diplomats and generals have argued.
Maintaining a nuclear capability could help deter threats to the UK’s security in future, their report concluded.
But they said continuous patrols could be relaxed while the UK must also show it is serious about working towards further international disarmament.
A final decision on whether to renew Trident will be taken in 2016.
The decision has been put back until after the 2015 elections following disagreements between the Conservatives and the Liberal Democrats.
While David Cameron supports the like-for-line renewal of the UK’s existing submarine-based ballistic missile system, the Lib Dems say the number of submarines could be reduced from four to three to save money.
Publishing its report, The Trident Commission said it believed that “retaining and deploying a nuclear arsenal” was necessary to protect the UK and to fulfil the country’s international responsibilities as a Nato member.
It said Trident met the “criteria of credibility, scale, survivability, reach and readiness” and alternative delivery options touted “simply on the basis of possible but speculative cost savings” should not be contemplated.
The commission’s members include former Conservative foreign secretary Sir Malcolm Rifkind, former Labour defence secretary Lord Browne and former Lib Dem leader Sir Menzies Campbell as well as former Chief of the Defence Staff Lord Guthrie and Sir Jeremy Greenstock, UK ambassador to the United Nations.
Their report stated that a nuclear capability should not be justified on the grounds of it being an “insurance policy” against an uncertain future or to maintain Britain’s diplomatic standing in the world.
The rationale for keeping Trident, it added, lay in its ability to counter “credible” threats to the UK’s security.
It identified three scenarios in which such threats could arise; from a long-standing nuclear state with an “aggressive posture”; from an existing or emerging nuclear state which “enters into direct strategic competition with the UK”; a “massive overwhelming” threat involving weapons of mass destruction.
“If there is more than a negligible chance that the possession of nuclear weapons might play a decisive future role in the defence of the UK and its allies in preventing nuclear blackmail, or in affecting the wider security context within which the UK sits, then they should be retained,” the report stated.
“The impact of the UK’s falling victim to ongoing strategic blackmail or nuclear attack is so significant that, even if the chances appear slim today, there is sufficient uncertainty surrounding the prospect that it would be imprudent to abandon system that have a high capacity to counter such threats.”
The commission was divided over the question of whether the current practice of always having one submarine at sea at any other time should be maintained.
Some members argued that continuous-at-sea patrolling should continue until there was an “improvement in the security environment” while others argued that without a direct threat to the UK’s interests, this could happen immediately while retaining the capacity for increased patrols at times of crisis.
But the commission was united in its call for the UK to consider what it could do to further the cause of nuclear disarmament and to discourage proliferation.
While acknowledging the steps that had been taken since the end of the Cold War, it said the UK could consider a further reduction in missile and warhead numbers, enhanced verification procedures and commitments to control or decrease stocks of fissile materials.
“The commission would recommend that the Ministry of Defence study the steps down the nuclear ladder more thoroughly to give greater confidence to the international community that we are considering such steps seriously in preparation for multilateral disarmament negotiations,” it said.