Last week, His Majesty’s (HM) Government published the long-awaited Defence Investment Plan (DIP) – the follow-up to 2025’s Strategic Defence Review (SDR). Backed by almost £300 billion, the DIP lays out how funding will be allocated to the British Armed Forces over the next four years.
However, the DIP has proved contentious within HM Government, having led to the resignations of John Healey and Al Carns as Secretary of State for Defence and Parliamentary Under-Secretary of State for the Armed Forces respectively over its shortfalls in defence funding. As Sir Keir Starmer has also announced his resignation as Prime Minister, this week’s Big Ask posits the following question to five experts: Should the next Prime Minister reopen the Defence Investment Plan?
Defence Director, ADS Group
The publication of the DIP provides long-awaited clarity for the United Kingdom’s (UK) defence sector after an extended period without a comprehensive equipment plan. While there is still more to do to meet the ambitions set out in the SDR fully, the DIP establishes an important foundation from which HM Government and industry can now build.
For industry, the priority should not be reopening the DIP, but delivering it. Stability and clarity are essential to enable businesses to invest in skills, facilities, innovation, and resilient supply chains that underpin sovereign capability. Frequent revisions to strategic priorities or funding allocations risk delaying programmes, increasing costs, and weakening industry confidence at a time when the global security environment demands greater pace.
The next Prime Minister should therefore ensure the full delivery of the DIP while building out a credible, fully funded roadmap to increase defence spending to 3% of Gross Domestic Product (GDP) by 2030 and 3.5% by 2035, consistent with Britain’s North Atlantic Treaty Organisation (NATO) commitments. Such a roadmap should provide clear milestones, sustained investment profiles, and confidence that today’s commitments will translate into tomorrow’s capabilities.
The focus should now shift from debating the settlement to accelerating delivery. Converting investment decisions into contracts, reforming procurement, strengthening export potential, and building long-term industrial capacity will ensure that the UK maximises the return on every pound invested. Industry stands ready to partner with HM Government to turn strategic ambition into enduring military capability and economic growth.
Research Fellow (National Security), Council on Geostrategy
The answer is both no and yes.
No, because it has taken over two years of defence, national security, and investment reviewing and planning to get to the point that the DIP could be published in the first place. A reopening of the entire process risks months of delay, where major contracts might be pushed back at a time when British defence requirements and defence firms are desperate for movement from Whitehall. Starting from scratch, tempting as it may be, could cause another several-month period of drip-feeding investment.
With that said, it is evident that the DIP as it stands is below what is needed to meet the threat environment and the UK’s commitments to NATO, with many of the key investment decisions delayed to the 2030s. The next Prime Minister should overrule Treasury objections and force through – ideally with cross-partisan support – a clear and appropriate financial settlement. A year-on-year incremental increase in percentage of GDP from now to 2035, roughly 0.14 percentage points each year, should be agreed to deliver certainty.
With this agreed to, a ‘bolt-on’ to the DIP can be worked towards. This should be far more concise, plainer in language, and simply outline additional investments planned with this further uplift in spending. The air and maritime domains should be the focus, to complement the growing land domain capabilities of European allies and backfill the presumed withdrawal of American air and naval assets needed for deterrence in the Indo-Pacific.
Member, Defence Committee
Should the next Prime Minister reopen the DIP? Indisputably. Two-thirds of the DIP is unfunded, the remaining third is insufficient, and together they sign the Royal Navy’s death warrant.
The DIP fails HM Government’s threat assessment. Sir Keir says that Russia could attack NATO by 2030, yet the funded third of the plan expires that year. It requires finding £4.7 billion at the Budget and £10.7 billion in ‘efficiencies’ on a scale that the Ministry of Defence (MOD) has never achieved. Two-thirds of the investment falls after 2030 and is unallocated, subject to next year’s spending review.
Worst of all, the DIP kills the Royal Navy as we know it. The UK will end this year with five frigates, and the DIP accelerates their retirement to 2033. Their replacements will arrive after 2030, meaning the country’s frigates retire on a fixed schedule while their replacements arrive on an unfunded one. By my maths, Britain will have three frigates in 2030 – the moment of peak danger.
The UK’s destroyers will retire from 2035, and their replacement is the Common Combat Vessel (CCV), alongside other uncrewed ships. A hybrid fleet is admirable, but it only exists on PowerPoint and is unfunded, with the money coming after 2030. Expecting to get ships from PowerPoint to projecting power in nine years is implausible.
The intelligence is unequivocal: Britain must be ready for war by 2030. The new Prime Minister should scrap the Global Combat Air Programme (GCAP) to invest £8.6 billion in the fleet, fund the entire plan at the Budget, and pull every timeline to this side of 2030. Anything else would be negligent.
Adjunct Fellow, Council on Geostrategy
The DIP was designed to be ‘scalable’. Like the classic Greek family villa, you can build the first storey and leave the second as a bunch of iron rods protruding from the concrete until you find enough money to complete it.
So, the general design of the DIP should not be reopened. By going for a hybrid navy; a Ukraine-style uncrewed systems taskforce; and backing AUKUS, GCAP, and the Continuous At-Sea Deterrent (CASD), plus nearly £2 billion for a digital targeting web, HM Government has made the right choices.
However, there is an obvious missing piece with Integrated Air and Missile Defence (IAMD), and that is the ‘second storey’ I would build if the money becomes available. The critical milestone is now the 2027 Spending Review. The defence sector needs to win the argument with politicians, the public, and HM Treasury that a verbal commitment to spending 3.5% of GDP by 2035, backed by a fiscal commitment to just 3%, is not sustainable.
Rob Murray
Honorary Fellow, Council on Geostrategy
Yes. Reopen the DIP. Then throw away the thinking behind it.
The SDR answered the first question: What threats does the UK face, and what capabilities does it need? The DIP tried to answer the second: How does Britain pay for them? In this, it failed.
The DIP did not fail because HM Treasury cannot count. Rather, it is because the UK is trying to prepare to fight a 21st century war with a 20th century financing model. Britain made the strategic mistake every successful organisation fears: it put the Chief Financial Officer (CFO) in charge.
HM Treasury should not decide how much security the UK can afford. It should figure out how to afford the security that the country needs. Stop asking what drones will be needed in 2035. Nobody knows. Ask one question instead: what outcomes must Britain always deliver?
The objectives laid out by the Chief Executive Officer (CEO) – i.e., the Prime Minister – to the defence chiefs should be: deter war, win if deterrence fails, out-build the UK’s adversaries, and adapt faster than they can.
The next step is to finance those outcomes. Britain has already committed to spending up to 5% of GDP on defence and security. The issue is not whether it spends more. It is whether it mobilises capital intelligently.
No great company finances transformation from cash flow alone. It mobilises capital. Nations should too. This is not financial engineering. It is how every successful multilateral bank creates fiscal space. Defence should not be the exception.
Wars are not won by defence budgets. They are won by financing systems that can out-build the other side. Capital has become a weapon of national power. The UK should start treating it like one.
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What do you think about the perspectives put forward in this Big Ask? Why not leave a comment below?
Almost all of it is well reasoned except I cannot fathom why Mike Martin wants to give up GCAP/Tempest. The UK should give up its aerospace industry? Abandon Japan and Italy? Discontinue what is likely to be its most successful defense export program? This is crazy. It’s Britain’s number two defense priority. He is right about the Royal Navy needing a lot more money.
I’m not convinced we measure or define things properly. I agree with Michael, we need a fully defined force for both the current/immediate future as well as for the long term future defence. But also I feel we need to break away from percentage spending. Surely the defined need will stay the same regardless of how well or poorly our economy is performing and therefore a set figure that can rise with inflation would be a better way to budget.