Debate over the renewal of the Trident nuclear programme is set to become even more intense after the Ministry of Defence disclosed the costs have jumped by billions of pounds.

David Cameron, announcing the outcome of the five-year strategic and security review in the Commons, pledged to maintain nuclear weapons as “our ultimate insurance policy as a nation” but failed to mention the new estimated cost.

The strategy document disclosed the cost of the proposed four nuclear submarines at £31bn, up from a projected cost of £25bn five years ago and £20bn in 2006.

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The rapid rise will add to the already combustible argument over the UK’s nuclear programme ahead of a Commons vote due to be held next year on whether to renew Trident. The first of the submarines is not due to come into service until the early 2030s.

The review said a contingency of £10bn would also be set aside, suggesting the MoD fears the costs could rise beyond the £31bn estimate.

The Trident figure was one of the few elements of the strategic defence review that had not been revealed in advance. Downing Street said that the costs had increased after the completion of the design phase of the renewal programme. The prime minister’s spokeswoman said: “That reflects the fact that we have now gone through the design phase, we’ve got a better idea of costs and timescales. That is an update on the 2011 figure, which was £25bn.”

The government also confirmed in its defence review that the introduction of the new generation of Successor Trident submarines is to be delayed by up to five years. The phasing out of the current fleet of nuclear-armed Vanguard submarines, which had been due to take place in 2028, has been put back to the early 2030s. The prime minister said that a parliamentary vote will be held on the “maingate decision”. But Downing Street declined to say whether this would be held as originally planned in 2016.

The MoD is to spend £178bn over the next decade on weapons and equipment, of which £12bn is extra money. The Cabinet Office found £11bn in savings from the MoD, the security and intelligence agencies and counter-terrorism spending.

Much of the 94-page report deals not with defence issues but with fears over a terrorist attack. It says that 10,000 troops will be available to help police in the event of a major terrorist incident, double the previous figure.

The prime minister told MPs: “Just as in France it was necessary to surge the number of uniformed personnel on to the streets to sometimes provide a security cordon or keep people safe, we should get rid of the divide that there has been for many years about the deployment of military personnel on the streets of Britain. The first 5,000 are all ready to fulfil that function ... This is not about supplanting or taking over from the police. It is being there at the disposal of the police.”

The defence review also says that:

• New equipment and weapons will be made available for the special forces, the Special Air Service (SAS) and the Special Boat Service (SBS). This will include a weaponised Zephyr drone that is capable of remaining in the air for months.

• A 50,000-strong expeditionary force will be formed by 2025 for deployment in crisis spots such as the Middle East. They are not extra troops but drawn from existing forces.

• One of the costliest items will be planes for two new aircraft carriers. The review is proposing 28 F-35s at a cost of £100m each, fewer than when the carriers were first proposed.



• The army, navy and air force stay roughly the same in terms of personnel – up from 141,390 to 144,350 over the next five years – but civilian defence staff are to be cut from 56,860 to 41,000.

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The introduction to the report says: “The world is changing rapidly and fundamentally. We are seeing long-term shifts in the balance of global economic and military power, increasing competition between states, and the emergence of more powerful non-state actors. We are increasingly likely to have to deal with unexpected developments.”



It adds: “The threat from Islamist terrorist groups to the UK, including to British nationals and interests overseas, has increased. Since 2010, over 60 British nationals have been killed as victims of terrorism overseas, including in the recent attacks in Sousse and Paris. The terrorist threat is fed, supported and sanctioned by extremist ideologies.”

The nuclear issue is the most politically divisive of those covered by the review, with the Labour leader, Jeremy Corbyn, and the Scottish National party opposed to the renewal of Trident.



The MoD has provided no overall total for Trident, only the cost of renewing the submarines. Also to be taken into account are missiles, warheads, anti-submarine vessels, infrastructure and personnel.

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Kate Hudson, the CND general secretary, described the new figures as outrageous, and suggested the total for Trident renewal could rise to a staggering £182bn, taking into account the £31bn, the contingency fund and other costs. “In its determination to replace this cold war relic, the government is prepared to keep on spending, even if it’s to the detriment of conventional forces and tackling the real security threats we face, such as terrorism, cyberwarfare and climate change,” she said.



There was some confusion over the defence review’s statement that the government was simply committed to holding a debate in parliament on the renewal of Trident. The government originally said that it would hold a vote on the “maingate decision” – a decision on total investment, the point of no return – by next year.



The prime minister told the Tory chairman of the Commons defence select committee, Julian Lewis, that MPs would have a vote. Cameron said: “The maingate decision: we will be moving ahead with the four submarines and obviously at the appropriate moment we will want to have a vote in this house.” The prime minister later added: “I’m very keen that we have a vote.”

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Corbyn challenged Cameron over the planned cuts to police numbers, which are due to be announced in the spending review on Wednesday. The Labour leader also said that the party’s defence review would assess whether it was right to devote such a large part of the defence budget to the Trident replacement.

The prime minister mocked Corbyn for voicing support for the armed forces when he questioned the need for having large armed forces during the Labour leadership contest. “I know it is depressing for people sitting opposite but they might as well know about it,” Cameron said. “That is the view of the leader of the opposition.”

Andy Burnham, the shadow home secretary, raised concerns that the deployment of 10,000 troops in a “surge” to help police in response to a terrorist incident could be used to mask cuts to police numbers. Burnham told the Guardian: “This would represent a significant change in the way we respond to serious incidents. I don’t think the prime minister has made the argument that it is safe to cut the police and ask the military to fill the gaps.

“What if those military personnel are required overseas? It seems as though the government has chosen to invest in the military and take the money from the police force. I don’t think that will strike the public as the best way to keep us safe.”

In other announcements, the government said eight Type-26 frigates will be built on the Clyde, nine new surveillance planes will be based at Lossiemouth in Scotland to counter Russian air and submarine activity around UK airspace and water, and the number of Typhoon aircraft is to be extended for an extra 10 years to 2040, meaning there will be a total of seven frontline squadrons, with about 12 planes per squadron.