We are increasingly concerned that the Labour party’s defence review is sliding into chaos and incoherence. We accept that there is a legitimate disagreement as to whether the United Kingdom requires an independent nuclear deterrent.

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Given the increased prominence of nuclear weapons in the security policies of Russia, China and North Korea, the significant nuclear weapons building programmes occurring in those countries, and the strident brandishment of those weapons as official policies there, it is self-evident that a British nuclear deterrent will be essential to our security for decades to come.

We understand, of course, that there is another point of view, although we strongly disagree with it. But we do not accept as legitimate the use of spurious arguments and newly created “facts” to argue against the plan to continue the deterrent into the future by building four new ballistic-missile submarines.

The question of how to maintain a British nuclear deterrent into the mid-century has been studied exhaustively over the past 10 years. The Blair government conducted the original “deep dive” in 2006, resulting in a white paper, approved by parliament, recommending building new submarines. The coalition government, pressed by the Lib Dems, conducted an extremely detailed Trident Alternatives Review in 2013. The British-American Security Information Council (Basic) convened an extraordinary panel of independent all-party experts that made its report in 2014.

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All these studies concluded that a deterrent carried by ballistic missile submarines provided the greatest deterrent capability at least cost.

To be clear, all other potential deterrent platforms were evaluated. Land-based missiles, land-based aircraft and carrier-based aircraft were rejected because of their lack of survivability, and, in the case of land-and-sea-based aircraft, their relatively short range. In addition the F-35s Britain is acquiring lack a nuclear weapons capability and the UK does not have an air-delivered nuclear weapon in its inventory. Equipping Astute-class attack submarines with cruise missiles appeared superficially attractive, until it was recognised that to fill this role the Astutes would need major (and very expensive) hull redesign to carry cruise missiles. A much larger than planned Astute force would be needed, as would the development, testing and production both of cruise missiles and a new warhead for them.

Trident submarines, on the other hand, are highly survivable and carry the existing Trident II missile, which we possess under a financially advantageous arrangement with the United States. The Trident II will carry the UK’s current nuclear warheads. It is, therefore, a flight of fancy to suggest that a viable alternative to the existing submarine model exists.

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All of this said, two new – and completely spurious – accusations have been raised by some involved in the Labour review intended to cast doubt on the continuous-at-sea option. The first is the contention that the submarines could be disabled by cyber attacks. To the degree a cyber threat exists, it applies to any deterrent platform (or, indeed, to any military system). But the Trident boats are uniquely resistant to cyber attack.

If the concern is the nuclear command and control system, the fact is that the UK’s system is not connected to the internet (nor are there any plans to do so) and it is therefore impossible to introduce web-carried malware into it.

If the concern is the ship’s operating system, once the submarine is submerged internet viruses can’t enter the hull.

If the concern is cyber vulnerability while the submarine is pierside in Faslane, we can only assume that the operating system also will be “air-gapped” and that malware cannot be imported into it via the net.

That leaves sabotage, and we can only believe that every portal that provides entry into the operating system will be blocked or sealed to prevent the introduction of malware through the use of thumb drives or other such devices.

The second new concern that has been raised is that a new generation of underwater drones (or unmanned underwater vehicles - UUVs) will be able to seek out and destroy Trident submarines in the open ocean. UUVs, even future generations, will not have the range or sensors to conduct wide-area search. That means that they must be transported to the general area of the submarine by a mother ship or mother plane. In either case the submarine would hear the carrier platform enter the area, would hear the UUVs enter the water, and could take evasive action – just as it would if it detected a hostile submarine. All of this assumes, incorrectly, that the submarine has already been geo-located in a particular area, which brings us to the timeless question of the oceans turning transparent.

Every decade for at least the past 50 years predictions have been made that space-based or other non-acoustic sensors will turn the oceans “transparent”, thereby rendering submarines of all types vulnerable to detection, location and attack. Physics is a tough master however, and the oceans remain opaque. While we cannot rule out an eventual breakthrough, we are confident that the Successor class of Trident subs will be able to hide in the deep ocean, providing Britain with a powerful, invisible, secure and invulnerable deterrent for many years to come.

• Lord Robertson of Port Ellen and Lord Hutton of Furness are both former secretaries of state for defence. Lord Robertson was also secretary general of Nato and Lord Hutton is now a consultant for Lockheed Martin