Strategic Defence Review 2025: NATO

The Strategic Defence Review, published by the government on 2 June 2025, sets out a “NATO first” approach to UK defence.

Note that the term ‘UK defence’ is used here to refer to the Ministry of Defence and the armed forces collectively.

About the Strategic Defence Review

The Strategic Defence Review (SDR) was commissioned by the Labour government shortly after it took office in July 2024 and was published on 2 June 2025 as The Strategic Defence Review 2025 – Making Britain Safer: secure at home, strong abroad.

Independently led by former NATO Secretary General, Lord Robertson, the government has endorsed the “vision and direction” of the review and accepted all 62 of its recommendations. The other two lead reviewers were General Sir Richard Barrons, former Commander of Joint Forces Command, and Dr Fiona Hill, who was Deputy Assistant to the US President and Senior Director for European and Russian Affairs on the US National Security Council from 2017 to 2019.

Current threats

In a foreword to the Strategic Defence Review (SDR), the Defence Secretary, John Healey, writes: “the SDR signifies a landmark shift in our deterrence and defence: moving to warfighting readiness to deter threats and strengthen security in the Euro-Atlantic”.

The SDR sets out why UK defence needs to be transformed urgently, highlighting that the nation faces multiple threats for the first time since the end of the Cold War. Russia is described as an immediate and pressing threat.

As such, deterring and defending in the Euro-Atlantic is one of three roles assigned to UK defence in the SDR to meet the threats facing the UK. The other two roles are: defend, protect, and enhance the resilience of the UK, its Overseas Territories, and Crown Dependencies, and shape the global security environment.

‘NATO first’

When the Strategic Defence Review (SDR) was commissioned, the Defence Secretary, John Healey, directed the reviewers to look at “enhancing the UK’s contribution to the Alliance and sustaining a ‘NATO first’ defence policy”. He reiterated that approach in his foreword to the SDR, writing that: “our defence policy is ‘NATO first’”.

The review reflects the remit set by the Defence Secretary. A NATO-first approach, the reviewers explain, means putting the alliance first in all defence thinking. This, the SDR says, is different from previous practice, and will require an organisational and cultural change within defence and Whitehall:

The Alliance must be the starting point for how the Armed Forces are developed, organised, equipped, and trained in order to contribute to deterrence in the Euro-Atlantic, shaping the environment and potential adversaries’ thinking every day.

Fighting alongside NATO…

The SDR assumes that the UK should not expect to fight a major ‘peer’ military power alone. This is because NATO is “the bedrock of our defence”, with 31 other countries committed to collective security. 

Collective security is a reference to Article 5 of NATO’s founding treaty, which states that an armed attack against one or more of the alliance members in Europe or North America shall be considered an attack against them all.

A ‘peer’ adversary is defined in the SDR as a country that can match the UK’s military capability and/or that of its allies. Transforming UK defence from one that is “not currently optimised for warfare against a ‘peer’ military state” into one that is optimised to do so also underpins the entire SDR.

… but not always with NATO

The SDR is clear that the UK armed forces need to be capable of fighting alone, given its commitments and responsibilities beyond the Euro-Atlantic. The UK’s responsibilities to the Overseas Territories are explicitly mentioned. This means that the armed forces need to be capable of operating as an “integrated, sovereign force when needed”. The SDR encapsulates this requirement by saying that “a ‘NATO First’ approach does not mean ‘NATO only’.”

2.5% defence spending target

As a member of NATO, the UK has committed to spending 2% of gross domestic product (GDP) on defence expenditure that meets NATO’s definition each year, reflecting a long-standing spending target of the alliance.

In February 2025, the Prime Minister committed to increasing defence spending to 2.5% of GDP by 2027 and to 3% in the next Parliament, when fiscal and economic conditions allow.

The reviewers explicitly referred to the February 2025 commitment in their foreword to the SDR, suggesting that without such a commitment the armed forces would have likely been required to cut capabilities.

The SDR says that, with additional resources, or if circumstances change, the transformation of defence could be accelerated faster than the ten-year timescale currently envisaged.

NATO’s Secretary General, Mark Rutte, expects allies to agree to increase the spending pledge to 5% of GDP at its next summit in The Hague, which will start on 24 June 2025. Rutte said he wants allies to set a “credible path” to 5% at the summit, including a clear end date for achievement.

About this briefing

This briefing sets out what the Strategic Defenc Review said about the UK’s relationship with NATO and what a ‘NATO First’ approach means for UK defence. It is one of a series of Commons Library research briefings examining the Strategic Defence Review.