A former Conservative defence secretary has said having a nuclear deterrent no longer guarantees the UK a place at the "top table" of nations.
Lord King said ministers had to think "very carefully" whether a like-for-like replacement for Trident was strategically necessary or affordable.
While he backed retaining a capability, he said nuclear weapons were not "god's gift" to resolving modern conflicts.
Prime Minister David Cameron has said he is committed to replacing Trident.
The government has set aside £3bn to start work on the replacement of the UK's fleet of four Trident nuclear submarines by 2028.
However, a final decision on a like-for-like replacement for the continuous at-sea weapons system will not be taken until after the next general election with the Liberal Democrats arguing that a cheaper alternative should be pursued.
Speaking in a Lords debate on nuclear disarmament, Lord King - defence secretary under John Major - said the world was "an extraordinarily dangerous" place and the UK faced multiple threats from terrorism, Islamist extremism, piracy and cyber crime.
But he warned that "against none of those does nuclear weapons look like the god's gift to solving the problem".
"Certainly it is not obvious to me that there is any need any longer for a major nuclear system based on 24-hour, seven day a week availability," he said.
Lord King, who advised David Cameron on defence matters when he was opposition leader, said the UK would be wise not to "totally abandon" its capability given global instability and the nuclear ambitions of other nations such as North Korea, Iran and Pakistan.
And a government considering "dismantling" Trident would face a major challenge in explaining the decision to the public, he added.
But he said he was no longer convinced by the argument that a nuclear deterrent gave the UK more diplomatic and military clout.
"I think in the current world we live in, top table credibility comes from availability to help in peace-keeping, in conflict resolution and having armed forces that can exist, co-ordinate and co-operate in the new high-tech, highly sophisticated systems."
Experts say maintaining a continuous at-sea deterrent for the next generation will cost between £25bn and £100bn.
In a "stringent" economic climate, Lord King suggested committing to a multi-billion pound renewal programme may stop the UK from meeting other responsibilities, such as contributing troops to UN peace-keeping missions.
"Playing our part in the world means that we must review very carefully to see whether we can find an alternative way forward which preserves our defences adequately but not at such an appalling expense," he concluded.
For the government, Foreign Office minister Baroness Warsi said the UK was committed to the goal of a world without nuclear weapons and successive governments had played a role in helping to cut nuclear arsenals.
"While there continues to be significant risks of further proliferation and other states retain much larger nuclear weapons arsenals, successive governments have been clear the UK will retain a minimum credible deterrent as the ultimate guarantee of our security."
MPs had approved the decision to press ahead with Trident renewal in 2007 and this remained government policy, she added.