The government's review of the future of the Trident submarine nuclear missile system is likely to suggest a significant downgrading of the UK's nuclear deterrent, including the possibility of locking the warheads "in a cupboard" for delayed launch only after several weeks of mounting international tension.

The revelation was made by Sir Nick Harvey, the Liberal Democrat who was the defence minister leading the review until the government reshuffle this month. The MP for North Devon said he believed the policy could get support in Whitehall and from senior military figures and Labour.

Harvey said past policy on Trident had been dictated by the 1980s view that the only deterrent to a nuclear attack from the then Soviet Union was the belief that the UK could "flatten Moscow" in retaliation. This led to the UK building Trident and having at least one armed submarine at sea every hour of every day since.

Speaking in detail about the Trident review for the first time since he was sacked as minister, Harvey said: "If you can just break yourself out of that frankly almost lunatic mindset for a second, all sorts of alternatives start to look possible, indeed credible."

He continued: "The Russia of the 21st century – economically diverse, vaguely democratic, but definitely a very different sort of place from where it was in 1980 – might find all sorts of damage to be unacceptable short of flattening Moscow.

"Therefore to convince ourselves that the only point of having any deterrent at all is the capability of flattening Moscow is the wrong and distorting lens through which to view the debate."

Instead of replacing Trident with a like-for-like 24-hour nuclear armed submarine presence at sea after the current system is due to be taken out of service in 2028, cheaper alternatives are being considered. These range from stepping down the patrols, to designing missiles to be launched from aircraft, surface navy ships or land, to a delayed launch system.

The delayed-launch model would involve developing a nuclear warhead for a cruise missile that could be launched from existing Astute submarines, Harvey said, "but having perfected that technology simply put it away in a cupboard and keep it as a contingency in case there ever were to be a deterioration in the global security picture that might need the UK government to take it out of the cupboard".

In this situation, the UK would store the warheads in a secure military location, from where they could be removed, put on the tip of a missile and put to sea within weeks or months.

Challenged as to why the review did not consider nuclear disarmament, Harvey said: "I think you might struggle to persuade the British public to do that, but I think you might persuade them to go down to the penultimate step: you keep something for a rainy day, but putting it away and not having it as part of your everyday activity."

Harvey told a fringe debate at the Liberal Democrat conference in Brighton that the idea of moving "down the nuclear ladder" had support across all three armed services: the army, the Royal Navy and the RAF.

He said one reason for growing support for the review's alternatives was a "perfect storm" of defence capital costs around 2020, including building the new joint strike fighter aircraft and Type 26 frigates, a new generation of unmanned aircraft, and amphibious craft for the navy.

The army, he said, was "driving around in vehicles which are literally about to fall to pieces".

If defence ministers in 2020 were not to be put in an impossible position, the defence ministers of the next couple of years would have to take the necessary decisions to avert a crisis.

He said: "Believe you me there are very senior figures of all three services who are highly aware of that perfect storm of these costs, who don't believe the Treasury is going suddenly ride to their rescue with a cheque and who are asking, 'Is the opportunity cost of having another generation of nuclear weapons too high, in terms of of what it would prevent us doing on other fronts?'"

He added: "I can't say with certainty how they [military chiefs] will respond, but a number of them made the point to me to not portray it [the report] in such a political and party way that you don't create the space for some of us to support you and try and help."

It was not impossible that the review could get support from the Whitehall security sector, said Harvey, who was also hopeful that Labour, or parts of the party, would support the review's conclusion.

He added: "The UK national security strategy no longer even identifies the nuclear menace as a tier one threat."

In a sign of the potential political row brewing over Trident, John Woodcock, the Labour MP for Barrow in Furness, where new Trident subs would be built, this week accused the Lib Dems of being in a "hopeless muddle" over the issue.

"The Lib Dems are either cosmically ill-informed or seeking to pull the wool over the eyes of many thousands whose jobs depend on a thriving shipyard," he said.

Harvey's response was that creating jobs in Barrow should be the last consideration. "The idea that you should produce weapons of mass destruction in order to keep 1,500 jobs going in the Barrow shipyard is palpably ludicrous. We could give them all a couple of million quid and send them to the Bahamas for the rest of their lives , and the world would be a much better place, and we would have saved a lot of money," he said.

"I had wanted my legacy to be bringing the UK down the nuclear ladder," added Harvey, who was knighted after his dismissal in the reshuffle.

However, Professor Malcolm Chalmers, research director at the defence think-tank Royal United Services Institute (RUSI), raised concerns about possible savings by scrapping a Trident replacement, saying he was not yet convinced by the figures.

"If you end up going for an option which steps down the ladder but you don't save any money it's a political non-starter," he said.

The review was made part of the coalition agreement between the Lib Dems and the Conservatives after the 2010 election because the two parties disagreed strongly on the issue. After Labour decided in 2007 to replace Trident with a like-for-like system, the Lib Dems went into the 2010 general election opposing that policy while the Tories supported it.

The review is now being headed by Danny Alexander, the chief secretary to the Treasury, who is a Lib Dem.

• This article was amended on 27 September 2012 to remove a reference to the UK adopting "a delayed launch system on the model employed by other countries, including Japan". This was intended to be a reference to the theoretical possibility that Japan could manufacture a nuclear weapon quickly because of its highly developed domestic nuclear industry, rather than a suggestion that it possesses nuclear weapons now. The Japanese embassy has asked us to point out that "Japan is firmly committed to its three non-nuclear principles of not possessing, not producing and not permitting the introduction of nuclear weapons, in line with Japan's peace constitution".