Sources say Britain will likely agree to Nato’s call to boost defence spending to 3.5% of GDP by 2035 ahead of this month’s summit, despite Starmer’s cautious public stance.

Britain is expected to commit to raising its defence spending to 3.5% of GDP by 2035 at the upcoming Nato summit, insiders say, as the alliance seeks to keep US President Donald Trump engaged. This would be a significant increase above the current Labour government’s plans and reflects pressure from Nato secretary general Mark Rutte, who has been negotiating closely with Trump.

A senior defence source told The Guardian the UK would “without a doubt” sign up to Rutte’s proposal, which would represent an increase of around £30 billion in real terms from current projections. The move comes despite Prime Minister Keir Starmer’s reluctance to commit publicly to a firm timetable for reaching even the 3% spending target he announced during Monday’s strategic defence review launch.

Currently, the UK spends 2.33% of GDP on defence. Starmer’s plan calls for a rise to 2.5% by 2027 and to 3% in the next parliamentary term. However, Nato’s new target, driven by Rutte and aimed at satisfying Trump’s demands, sets a combined defence and military-related infrastructure target of 5% of GDP, with 3.5% earmarked specifically for “hard defence.”

Last week, Rutte, a former Dutch prime minister, said he expected Nato leaders to agree to a “high defence spend target” in The Hague, where Trump will attend his first Nato summit of his second presidential term. He noted that the 3.5% figure would cover “hard spending,” while the additional 1.5% could include cyber, intelligence, and military infrastructure costs.

Downing Street declined to comment on the specific target on Tuesday but pointed to Starmer’s remarks during a visit to the BAE shipyard in Glasgow. The prime minister indicated an openness to ongoing discussions about the UK’s contribution as part of Nato’s future effectiveness.

The increased target is partly a political effort to keep Trump from disrupting the alliance, as he has repeatedly criticised Nato members for not meeting spending obligations. Trump previously threatened to quit Nato over defence payments and has demanded allies increase spending to as much as 5% of GDP—far above the current US rate of approximately 3.4%.

Rutte’s proposal reflects a compromise, allowing some flexibility in how Nato allies count their spending. The additional 1.5% target may include commercial infrastructure that supports military operations, broadening the scope of what counts as defence expenditure.

This broader interpretation could ease the UK’s challenge in meeting Nato’s demands but would still require significant budgetary adjustments. To fund the defence boost, the government might have to cut spending in other areas or raise taxes. Starmer has already hinted at possible reductions in the foreign aid budget, though this would only account for a small portion of the needed increase.

Defence Secretary John Healey emphasised on Tuesday evening that discussions about defence funding would take place at the summit and stressed the UK’s “huge contribution” to Nato. He said the summit would address more than just money, highlighting the UK’s commitment to bearing a greater share of Nato’s responsibilities.

Sources praised Rutte for his diplomatic efforts in maintaining Nato unity, particularly his ability to work with Trump through personal meetings in Florida and at the White House earlier this year. His steady leadership is seen as crucial to navigating the complex political landscape as the alliance faces both external threats and internal divisions.

For the UK government, the challenge lies in balancing Nato commitments with domestic fiscal pressures, especially amid calls for austerity in other public spending areas. However, the political imperative of backing Nato—especially under a “Nato-first” defence strategy—means Starmer is unlikely to resist the push for higher defence budgets.

As Nato leaders prepare to convene, the UK’s defence spending trajectory looks set for a steep climb, underscoring the alliance’s shifting priorities and the ongoing influence of US politics on European security policy.