The UK’s New Nuclear Warhead: Issues for Parliament

House of Commons Chamber. Courtesy of UK Parliament/Open Parliament Licence v3.0.

The UK’s replacement nuclear warhead programme needs better scrutiny. Here’s what Parliament could do.

Shortly before Christmas, the Ministry of Defence (MoD) released its annual update to Parliament on the future of the UK’s nuclear deterrent. The document referred to the year’s most important development: the UK is embarking on the complicated and sensitive task of building a new nuclear warhead – something it has not done for 30 years, and has never done without nuclear-explosive testing, which it has now foresworn. 

The update revealed little about this project that had not already been announced, which itself does not amount to very much. What we do know, however, is that the UK is building billions of pounds’ worth of new defence-nuclear infrastructure; the warhead will be produced in cooperation with the US, which has its own priorities and constraints; and the government has said that the new warhead programme will remain compliant with the UK’s commitments to non-proliferation and disarmament. This is a topic for rigorous parliamentary scrutiny, and although in recent months Parliament has shown interest, there remains more work to be done. 


Context helps clarify the stakes. In February 2020, the government announced that it is replacing the warhead currently deployed on the UK’s submarine-launched Trident missiles. The government says the replacement may be needed by the late 2030s; past estimates suggest it will take 17 years to develop and begin production, so the timeline is potentially tight. The new UK warhead will be developed in parallel with a proposed new US warhead, called the W93, and use a US-developed re-entry vehicle, the Mk7. In April 2020, Defence Secretary Ben Wallace wrote to Congress calling the W93 programme ‘critical … to the long-term viability of the UK’s nuclear deterrent’. The W93 programme has recently been approved by Congress, but could be delayed by the incoming Joe Biden administration. Meanwhile, the Atomic Weapons Establishment (AWE), which builds and maintains the UK’s warheads, has been facing significant challenges, including infrastructure delays and budget overruns, and will soon be brought back under the full control of the MoD.

Asking the Right Questions

There are five big themes on which Parliament should focus. 

First is the basic rationale for building a new warhead. Could the existing design not just be remanufactured? If not, why not? 

Second, what requirements will shape the new warhead, including military needs, reliability and safety upgrades, and potential future arms control and disarmament measures? What effect might these requirements have on the UK’s plans for new or updated nuclear infrastructure?

Third, what are the implications of dependence on US decisions, especially those relating to the W93/Mk7 programme? What is the backup plan in case of any disruption? 

Fourth, are the MoD and AWE set up properly to execute this programme, especially now that AWE’s arrangements are changing? 

Last but not least, how much will it all cost?

Secrecy and Scrutiny

The government has good reason to keep many details about the new warhead highly classified – above all, anything that could give adversaries an advantage, or anything that could encourage proliferation. But this does not include everything about the replacement programme, such as how this large and complex project will be managed and paid for. Nor should MPs assume that closer scrutiny is the sole preserve of those who oppose nuclear weapons. Supporters of the deterrent have an obvious interest in making sure it is effectively sustained, and the government has a poor record in delivering major projects, including large defence procurement projects. Moreover, the House of Commons voted by a large margin in 2016 to maintain continuous at-sea deterrence; work is well underway to build the next generation of ballistic-missile submarines; and both major parties (and their leaders) support renewing the deterrent. In this political context, the government can hardly claim that closer scrutiny of the warhead project poses an existential threat to the future of the UK’s nuclear force. MPs without strong views either way on the strategic case for nuclear weapons, for their part, should simply ask themselves whether they are happy for a multi-billion-pound, multi-year public sector project to go ahead without proper parliamentary scrutiny.

There is precedent to be found in the House of Commons Defence Committee’s regular inquiries into the Trident programme during the 1980s and early 1990s. Then, too, the government was initially reluctant to discuss warhead matters. But, by the late 1980s, the government’s approach had opened up considerably. The Committee took detailed evidence on the warhead for the newly procured Trident missiles and on infrastructure and staffing issues at AWE, including delays to the new A90 facility for the production of fissile components. In 1989, MoD officials and the then director of AWE gave substantive answers on a range of warhead-related questions, including production timelines for fissile components. 

The Committee’s work during this period was constructive and had practical impact. In its 1989 report, the Committee raised concerns that delays to A90 could mean that new warheads would not be available in time for the in-service dates of the second, third and fourth Vanguard-class submarines. This was acknowledged as a serious concern by the Thatcher government and even cited as the reason for its subsequent decision to contract out operations at AWE. This time around, Parliament should not wait for problems in the UK’s nuclear complex to become equally pressing. 

Making the Questions Stick

Individual MPs can continue to submit written questions to the MoD, though many are likely to be returned without substantive answers. The National Audit Office and the Public Accounts Committee have an important role to play in scrutinising major projects, and have already produced valuable work, such as on the new warhead assembly/disassembly facility, named Mensa. The clearest targets for further scrutiny of this sort are a planned enriched-uranium handling facility (Pegasus) and the joint UK–French hydrodynamic-radiographic project (Teutates Epure). 

Responsibility for the big questions of strategy, policy and management, however, falls primarily on the House of Commons Defence Committee (although the Lords International Relations and Defence Committee and the Joint Committee on the National Security Strategy might also take an interest). The Defence Committee could consider the following specific measures:

  1. Letters to the defence secretary: for example, asking for the benchmarks by which the MoD plans to judge success of the reorganisation at the AWE.
  2. Questions on warhead replacement during regular evidence sessions with the defence secretary, the minister for defence procurement and the MoD permanent secretary. The Committee did this in a recent session with the permanent secretary, with some important results, including confirmation that there is ‘a very close connection in design terms and in production terms’ between the US W93 and the new UK warhead programme. 
  3. One-off evidence sessions: for example, with the senior responsible owner (SRO) of the Nuclear Warhead Capability Sustainment Programme (the existing programme under which upgrades to the UK’s nuclear weapons infrastructure have been made). The current SRO was officially notified upon appointment, as is routine, that he would be held personally accountable to parliamentary select committees. He should be called to give evidence before the current AWE arrangements end in July 2021, to discuss the programme’s challenges to date and any improvements that need to be made.
  4. A post-appointment scrutiny session with the chair-designate of the new AWE board, John Manzoni. He should be asked for his vision for AWE reform, and for his thoughts on what has to happen for the new arrangements to be an improvement on the existing MoD–AWE relationship. 
  5. A full inquiry: for example, on ‘The Atomic Weapons Establishment: Strategy, Policy and Programmes’. This is an ambitious recommendation, and must compete with the other considerable demands on committee time. But given the stakes involved, it would be worth the investment. The Committee could also consider the establishment of a sub-committee on these issues.
  6. A Committee visit to AWE (coronavirus restrictions permitting). This would allow the Committee to hear for themselves the technical and personnel challenges involved in this project.


Given the need to protect national security, it would be reasonable for the government to ask Parliament to approach the topic delicately. The Defence Committee should be willing to hold private sessions on sensitive aspects, and publish transcripts only with government consent, redacted as needs be. 

This should not, of course, mean writing a blank cheque to the MoD to withhold details that are merely embarrassing, rather than national security-related. Parliament and government will need to develop a degree of trust on this topic such that constructive scrutiny can be carried out. Here, both sides can raise their game. 

The views expressed in this Commentary are the author's, and do not represent those of RUSI or any other institution.


Dr Matthew Harries

Former Director of Proliferation and Nuclear Policy

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