An update on UK nuclear weapons modernisation

This blog article is adapted from a talk given at the 2022 Student and Young Pugwash conference. It gives an overview of the costs and risks involved in the UK nuclear weapons modernisation programme. It also summarises recent research from Nuclear Information Service (NIS), and draws on the work of Peter Burt and Claire Mills.

NIS has estimated the total cost of replacing the UK’s nuclear weapon system between 2019 and 2070 to be at least £172bn. It is a huge, national, multi-decade endeavour, with all four elements of the system being replaced. This includes the submarine, missile, warhead, and infrastructure.

The 2015 Strategic Defence and Security Review described building four new nuclear-armed submarines alone as “equivalent in scale to Crossrail or High Speed 2”. However, the UK Government’s centre of expertise for major projects has, for several years, warned that the nuclear enterprise is facing serious difficulties. The Infrastructure and Projects Authority’s last annual report stated that there had been no improvement in the status of the nuclear projects it reviewed over the previous year.

This article will discuss each element of this vexed programme in turn, beginning with the submarines.


Jon Thompson, former permanent secretary at the Ministry of Defence, was asked by MPs in 2015 which project troubled him most. He answered unambiguously: the new nuclear submarines. “The project is a monster,” he said. “It keeps me awake at night”, because it is the “single biggest future financial risk we face”.

Building four new submarines is the most expensive of the UK’s nuclear weapons projects. Parliament initially voted to begin the process of building a replacement for the UK’s Vanguard-class submarines in 2007. Work on the submarine programme, named Dreadnought, began in March that year.

At that point the first of the four new submarines were supposed to come into service from 2024. The estimated total cost of the project was £15–20bn. The programme moved into its delivery phase in July 2016 following a parliamentary vote.

As of 2022, work is under way on construction of the first two of the four planned new submarines. Procurement of long lead items for the last two submarines has also commenced. The first submarine is now expected to come into service in the early 2030s and will retire in the 2060s. The second delivery phase for Dreadnought was extended by a year due to the Covid-19 pandemic. At present the estimated total cost of the project has gone up to £31bn with a £10bn contingency.

The Dreadnought class will draw upon US submarine designs, so efforts have been made to bring the two nation’s replacement programmes in line. For example, the Dreadnought submarines will be powered by a new reactor design, the PWR3, which stands for pressurised water reactor.

The PWR3 is based on a US submarine reactor design and will run on Highly Enriched Uranium fuel. The reactors will be built at Rolls-Royce’s Raynesway factory in Derby. However, the company is struggling to upgrade the facilities which are needed to build the PWR3. In addition, the Government’s 2021 Defence Equipment plan stated that the manufacture of new reactor cores has been delayed by a year.

It is also important to appreciate that production of the UK’s nuclear weapons submarines is connected to production of the UK’s hunter killer submarines—known as Astute. All of the seven Astute submarines have faced severe delays, which contribute to the rising costs and risks of building Dreadnought.

Looking more widely, Professor Andy Stirling and Dr Phil Johnstone have highlighted how the UK’s nuclear weapons programme depends on civil nuclear energy production. This is because, they explain, the UK’s nuclear weapons infrastructure “relies on particular kinds of design expertise, engineering skills, supply chains and regulatory capabilities”. Calculating the true cost of the UK being a nuclear weapon state likely therefore requires us to include expenditure in the civil nuclear realm.

There are several other issues which impact on the UK’s ability to sustain its nuclear posture. These include: significantly extending the service life of the Vanguard class submarine; a fuel element breach issue in the PWR2 reactor design; and dock capacity at Devonport. These issues, and the way they interact with delays in the Submarine Dismantling Project, could jeopardise the Royal Navy’s ability to maintain constant nuclear submarine patrols, known as continuous at sea deterrence.


The UK’s nuclear warheads are delivered by Trident D5 missiles. These are US ballistic missiles to which the UK has access to a common pool. Previously, up to eight operational missiles were deployed on each of the UK’s Vanguard submarines. However, following the Government’s Integrated Review, published in March 2021, figures on the UK’s “operational stockpile, deployed warhead or deployed missile numbers” will no longer be made public, meaning that such numbers may rise.

The life extended version of the D5 missile began to be brought into service in 2017. There is scheduled to be a further life extension, which will last around twenty years, passing through concept, design and deployment phases. A review of this upgraded missile is expected in 2025, followed by ground testing and a first test flight in 2032, before early production begins.

These second life-extend version D5 missiles are set to be loaded onto UK Dreadnought submarines in the late 2030s. This is several years after the first of this new class of submarines comes into service. The focus of the life-extension programme is on developing technologies including: a post-boost control system; guidance instruments; radiation-hardened electronics; battery technologies; and cyber-security frameworks.

The missile compartment of the UK’s new Dreadnought submarines will be identical with the US’s own new Columbia-class submarines. The UK has paid for a significant proportion of the compartment’s development costs. This was because it was expected that the Dreadnought submarines would come into service ahead of the Columbia class, although this now appears unlikely.


In February 2020, US officials revealed the existence of a UK replacement warhead programme, which the British Government subsequently confirmed to parliament. The US disclosure led to accusations that the decision was taken without an official UK announcement or appropriate scrutiny. The Integrated Review included an announcement that the UK’s warhead stockpile cap would increase from under 225 to 260.

Given these concerning and retrograde developments, NIS is focusing on the UK’s next generation warhead. An in-depth analysis of this topic will be provided in a forthcoming report from NIS, currently being written by David Cullen.

Replacement of the UK’s current Holbrook warhead (with an upgraded Mk4A version) is thought to have begun in 2016. Monitoring group Nukewatch believe that the three Vanguard class submarines currently available for operational deployment have now been loaded with Mk4A warheads.

As with previous UK warheads, this upgrade is based on a US design. The Mk4A upgrade extends the life of the Holbrook warhead by around 30 years, meaning that it will remain in service until the late 2030s or early 2040s.

The Mk4A was designed as a staging post on the way to a full replacement warhead. New components in the Mk4A include the arming, fusing and firing system, the gas transfer system and new high explosives. The updated fuse allows more precision over the altitude of detonation and the accuracy of the weapon overall has been increased, making it more effective against hardened targets.

The Mk4A upgrade to the UK warhead is part of a wider project called the Nuclear Warhead Capability Sustainment Programme. The programme began in April 2008 and is due to run until April 2025. The total cost of the programme is currently projected to be around £20 billion. Along with the upgrade, this put in place infrastructure deemed necessary for the replacement warhead programme.

The UK’s replacement warhead is highly likely to be close in design to the US’s new W93 warhead. In addition, the contents of the US’s 2018 Nuclear Posture Review and the UK’s 2021 Integrated Review suggest that the UK’s new warhead will feature improved capabilities.

The UK Government has refused to give information about the timeline of the project citing national security, and has also not revealed details about its cost. However, based on previous timetables and estimates, it would seem that the replacement warhead is intended to come into service around the late 2030s or early 2040s. Regarding cost of the new warhead meanwhile, the BBC estimate this could be around £10 billion over the next 15 years, a figure similar to that previously estimated by NIS.

Much of the UK’s infrastructure for deploying, developing and building nuclear weapons is being rebuilt or refurbished. However, the UK’s Atomic Weapons Establishment, known as AWE, seems to exist in a state of near constant crisis.

In September 2020 AWE, previously operated as a government owned, commercially operated enterprise, was brought back into public ownership, owing to its poor performance record. Later that year the Chief Nuclear Inspector predicted that AWE Aldermaston would remain under enhanced regulatory attention until at least 2022 because of safety concerns. Most recently, labour disputes and the impact of Covid may have caused further delays to production.

In March 2021 the Ministry of Defence approved funding to restart the troubled Project Pegasus. This project involves building a new enriched uranium manufacturing facility at AWE Aldermaston. Work on the project had been paused over six years ago due to mismanagement, delays and cost overruns. The original project budget for the facility was £634 million, which the MOD are now very likely to exceed.

Several of the infrastructure projects the UK is engaged in relate to the techniques used for nuclear weapons development, in place of live explosive testing. For example, Project Mensa, which involves the construction of a new warhead assembly facility at AWE Burghfield, was approved a month before Pegasus. However, Mensa is delayed by six years and forecast to cost over £1bn more than its original budget. New joint Anglo-French hydrodynamic research facilities for warhead research work are also under construction in France under Project Teutates.

Other infrastructure being modernised includes:

  • Upgrades to the Trident submarine base at the Clyde Naval Base, which will cost £1.5 billion over the next ten years.
  • The construction of new facilities at the BAE Systems shipyard at Barrow-in-Furness where the Dreadnought submarines will be built. This is set to cost £300 million.
  • The construction of a new Core Production facility at Rolls-Royce’s Derby factory, where PWR3 reactor components will be produced. Around £1.8 billion has been allocated to this.

Concluding thoughts

Many projects within the UK’s nuclear weapons programme have gone vastly over their original budgets. New funding is being poured in to pay for the many projects within the programme facing cost increases.

The programme is also facing severe delays, raising serious questions about the UK’s ability to produce this weapons system. Such mounting pressures should be being thrown into sharp relief by developments elsewhere.

For example, the Treaty on the Prohibition of Nuclear Weapons has entered into force. Yet the UK did not participate in negotiations on the treaty and categorically stated that it will not sign or ratify it.

The Covid-19 pandemic has had a devastating impact on communities worldwide. Yet the UK is doubling down on military spending rather than prioritising a green recovery, or supporting a global peace dividend, as recently proposed by leading scientists.

As a party to the Nuclear Non-Proliferation Treaty the UK is committed to reducing the number of its nuclear weapons, and reducing their role in its security policies, pursuant to disarmament. Yet as the 2022 NPT Review Conference approaches, the story the UK has to tell is one of rearmament.

Much greater public and parliamentary scrutiny of the UK’s nuclear programme and wider militarisation is therefore needed. This is vital if there is to be any chance of the UK prioritising arms control, non-proliferation and disarmament.

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