The defence secretary, Michael Fallon, has dismissed Jeremy Corbyn’s proposed compromise on the Trident nuclear weapons programme in which submarines would be retained but go to sea without warheads as “pointless”, comparing it to going into a fight with an imitation gun.

Fallon was speaking after a tour of HMS Vigilant, one of the UK’s four submarines that carry Trident missiles capped with nuclear warheads, docked at Faslane naval base on the river Clyde in Scotland.

“If you are going to have a deterrent, you have to be prepared to use it,” he said, adding that he hoped a Labour review into the future of Trident would take into consideration the views of what he described as moderate Labour opinion.

“If Labour maintains this new position against the deterrent, clearly they are a threat to national security because it means we would be less safe under a future Labour government.

“I hope even now that their review, which is being led by a Labour leader who is anti-nuclear and a shadow defence secretary who is anti-nuclear, will listen to more moderate mainstream Labour voices.

“It’s extremely dangerous, it will undermine our alliances, weaken our standing in the world and would threaten our safety. It’s like making imitation rifles. Nuclear patrols would be pointless without nuclear weapons.”

The government has still to announce a date for a vote on the successor to the existing Trident fleet. Fallon, in a separate interview with television, initially said it would be held in a matter of weeks but quickly corrected himself to say a decision had still to be taken. Fallon said it would be held “shortly”.

The government believes it has enough votes to win on Trident, even in the face of Labour and Scottish National party opposition. The question for ministers is whether to hold the vote in the next two months before the May election campaigns get under way or prolong what they see as Labour’s mess on defence through to the autumn.

Submarines such as HMS Vigilant are to remain operational into at least the early 2030s, when a new generation of submarines is due to take over. It is these new subs that parliament will be voting on this year, theoretically because of the long time needed for design and construction.

Labour, after three decades of support for Trident, is conducting a review into whether it makes sense for the UK to continue to have nuclear weapons and on the practicality of investing so much, an estimated £31bn for the four new subs, at a time when fast-developing technology could make these subs obsolete.

Quantum computers, better surveillance, cybersecurity and underwater drones present a challenge to the ability of the submarines to remain hidden.

Fallon denied that the submarines were in danger of being obsolete by the time they became operational 15 years from now, provided they arrived on schedule. “These boats have been patrolling without being detected for 47 years. They patrol in isolation and are well equipped to escape detection,” he said,

He added that Trident was better able to protect the UK from unpredictable threats. No one had predicted the emergence of Islamic State, he said, and no one could be sure there would not be a nuclear threat in the next 30 years.

He expressed concern about Russia’s nuclear weapons programme, adding: “We are very concerned about nuclear weapons going to rogue states like North Korea.”