Two former Labour defence secretaries, Lord Robertson and Lord Hutton, have said the party’s defence review is “sliding into chaos and incoherence” and have rejected claims that new technology could make the Trident nuclear submarine obsolete.

In an article published in the Guardian, the two, both staunch defenders of the nuclear deterrent, dismissed as “spurious” arguments they said had been raised by some involved in the review, apparently referring to the new shadow defence secretary, Emily Thornberry.

Robertson and Hutton take issue with two arguments in particular that are gaining increasing currency: that Trident submarines could be disabled by cyber-attacks; and that underwater drones and other technological advances mean there is no guarantee the vessels could remain hidden in the future.

The peers’ article highlights the faultline running through Labour, especially the parliamentary party over the renewal of Trident.

After supporting unilateral nuclear disarmament in the 1980s, Labour’s policy since 1991 has been to support the UK’s nuclear weapons system. But Jeremy Corbyn, who is opposed to nuclear weapons, ordered a review soon after becoming leader in September. An interim review is expected to be completed by the summer, feeding into the party’s policy-making process. A vote on Trident is planned at party conference in the autumn.

Thornberry is conducting the review. In her first major speech since taking on the post at the start of the year, she told the Royal United Services Institute in London that the review was still in its early stages and no options had been ruled out.

But Thornberry said questions had to be asked not just about the cost of the four new submarines at an estimated £31bn but about technological advances in the next 20 to 30 years that could make them redundant.

“We must ask whether, if we are going to commit ourselves to the current platform for the next three decades, we can really be sure that it is future-proof,” she told the military thinktank. “But I also believe that we need to ask ourselves whether it is right to place our trust in one single weapons system to deter all threats and to protect us in all circumstances, and, if we do, whether the platform we currently have is necessarily the right one.”

The government, in its strategic defence defence review last year, committed itself to a replacement for the existing nuclear weapon system, with the new submarines scheduled to become operational in the early 2030s and form the core of British defence through to at least 2070.

A parliamentary vote has been pencilled in for later this year, with the government expected to win comfortably, with the help of some pro-Trident Labour MPs.

Senior British military staff shake their heads when asked about new technology making Trident submarines obsolete, as does the defence secretary, Michael Fallon.

But various thinktanks, particularly in the US, are sceptical about the ability to hide such a huge chunk of metal in the ocean in the future given the rise in the prevalence of underwater drones, which could be used to track submarines, improved surveillance and increasingly sophisticated cyberwarfare. If a Trident submarine cannot remain hidden, it loses its raison d’etre: it is supposed to be used to retaliate in the event of a nuclear strike on the UK.

Robertson, who was defence secretary in the Blair government and later was Nato secretary-general, and Hutton, who was defence secretary in the Brown government, wrote they did not accept as legitimate “the use of spurious arguments and self-created ‘facts’ to argue against the planned new submarines”.

On the threat of cyber-attacks, they said the UK nuclear command and control system was not connected to the internet and once a submarine was submerged internet viruses could not enter the hull. They assumed that malware could not be introduced while the submarine was docked and that steps had been taken to ensure portals were sealed to prevent sabotage through the insertion of a thumb-drive.

A YouGov poll of the views of Labour party members, published on Monday and commissioned by Election Data, suggested 68% were opposed to renewal of Trident with 18% in favour. Among those who joined after Corbyn became leader, the breakdown is 90% opposed, 6% in favour.

In a future Labour leadership contest, 51% said they could not support a candidate who voted for renewal of Trident, while 35% said they could.

The figures on Trident put the party at odds with the public, which, according to YouGov, is 46-28 in favour of renewal of Britain’s nuclear deterrent.

Defence and immigration are the two biggest issues on which the party is out of kilter with public opinion, according to the poll. Only 17% of party members view Trident as one of the top three issues facing the country. The issue lies in seventh place for members compared with the public, who make it the top issue.