The UK is rearming for deterrence—especially in the nuclear domain

21st June 2025

The UK isn't gearing up for war per se, but it is significantly reshaping its defence posture in response to what it calls the most serious and unpredictable threat landscape since the Cold War.

According to the 2025 Strategic Defence Review, the UK is moving toward "warfighting readiness"—a shift driven by growing Russian aggression, war in Europe, and emerging nuclear risks. This includes a major boost in defence spending: 2.5% of GDP by 2027, with an ambition to reach 3% in the next Parliament.

A big part of that investment is going into the Defence Nuclear Enterprise, which oversees the UK's nuclear deterrent. The government has reaffirmed its "triple lock" commitment to:

Building four new Dreadnought-class nuclear submarines,

Maintaining a 24/7 Continuous At-Sea Deterrent (CASD),

And delivering future upgrades to ensure safety and effectiveness.

There's also a £15 billion earmarked for a new nuclear warhead to replace the current Trident system, and discussions are underway about deeper UK involvement in NATO’s nuclear sharing arrangements.

So while this isn’t a march to war, it’s a clear signal that the UK is rearming for deterrence—especially in the nuclear domain—amid a more volatile global order.

The UK’s ramp-up stacks up against its NATO peers across two key axes—spending and doctrine:

Nuclear-weapons spending
• United States: ~$56.8 billion in 2024, the largest single-country outlay[1] • China (not NATO): ~$12.5 billion.

• United Kingdom: ~$10.4 billion, an increase of $2.2 billion year-on-year as it modernises and services long-term contracts.

• France: (Included in the "other nuclear-armed states" cluster; total non-U.S. and non-China spending was about $43 billion, implying mid-single-digit billions for France.

Conventional defense spending (2024) as % of GDP • Poland: 4.12% (highest) • Estonia: 3.43% • United States: 3.38% • Latvia, Greece, Lithuania: 3.1-3.0% • United Kingdom: 2.33% (NATO’s fourth-largest spender in absolute terms at $82.1 billion) • Germany, Italy, Canada: 1.3-2.1%[2]

NATO’s new investment benchmarks At the June 2025 Defence Ministers meeting, Allies agreed to aim for 5% of GDP on defense by the end of the decade—split into 3.5% on core capabilities (fighters, ships, etc.) and 1.5% on security-related investments (infrastructure, cyber resilience) to bolster collective deterrence and readiness[3].

Nuclear-deterrence postures.

• United States: “Supreme guarantee” via strategic triad and extended deterrence guarantees for all Allies. Foreign bases host U.S. warheads, and political control remains firmly in Washington[5]. • United Kingdom: Solely independent deterrent—four Dreadnought-class SSBNs under Continuous At-Sea Deterrent (CASD). No U.K. warheads are forward-deployed on Alliance soil[5].

France: Fully sovereign nuclear force (force de frappe), with no participation in NATO’s nuclear-sharing but cooperating politically through the Nuclear Planning Group[5].

• Other nuclear-sharing allies (Belgium, Germany, Italy, Netherlands, Turkey) host U.S. B61 gravity bombs under joint-use arrangements.

Summary While the UK’s overall defence burden (2.33% GDP) trails front-runners like Poland and Estonia, its £10.4 billion nuclear-weapons budget is only second to the U.S. globally and on par with China—reflecting London’s commitment to a credible, independent deterrent. By contrast, most European Allies combine conventional boosts with shared U.S. warheads rather than build sovereign arsenals. The Alliance’s collective ambition now pushes all members—and especially the UK—to close the gap on both spending and capability if NATO is to sustain credible, multidomain deterrence.

The most recent shifts in UK defence spending

Spending Review 2025
• Defence rises from 2.3% of GDP today to 2.6% by 2027, backed by an additional £11 billion of resource funding and £600 million for security/intelligence agencies.
• Capital budgets jump 7.3% through 2029—highlighting £4.5 billion for munitions (7,000+ missiles replenished) and over £6 billion to boost nuclear-submarine production. Day-to-day “running” costs creep up just 0.7% in the same period.

Nuclear-deterrent costs under the microscope
• A Public Accounts Committee report warns the Defence Nuclear Enterprise (DNE) now commands nearly £10.9 billion in 2024–25 (≈18% of total MoD budget), with ten-year forecasts ballooning to ~£128 billion—up from £117.8 billion last year.

• MPs fear overruns on Dreadnought-submarine builds and warhead R&D will “squeeze” conventional capabilities, urging the MoD to publish a new five-year equipment plan for transparency.

NATO spending target negotiations
• London is pushing back on a proposed 5% GDP defence-spending cap by 2032, proposing instead a 2035 deadline with a 2029 mid-term review.

• The UK remains on track for 2.5% of GDP by 2027, with a stated “ambition” of 3% in the early 2030s—well above Belgium/Canada (~1.3%) but below front-runners like Poland (>4%) and the US (3.4%).

Strategic Defence Review (SDR) follow-through • Published June 2025, the SDR commits to the largest overhaul of UK forces in 150 years—blending drones, autonomous platforms, a sixth-generation fighter, plus new missile-manufacturing plants.

• Delivering all 62 SDR recommendations will demand defence outlays hitting roughly 3.5% of GDP by 2034, underpinned by cuts to overseas aid and a phased multi-year funding settlement (2025/26 set, 2026–28 to be finalised in June 2025)