Starmer and the Fragile Foundation of a Quasi-Alliance

British Prime Minister Keir Starmer visited Japan on January 31 and agreed with Prime Minister Sanae Takaichi to further deepen bilateral relations. 

Since the Meiji Restoration, Japan has built particularly close ties with the United Kingdom as it pursued modernization and engagement with the outside world. Despite the hostilities of World War II, Japan-UK relations have evolved into what is now often described as a quasi-alliance, marked by close cooperation in security, economics, and trade.

"This relationship is the strongest it has been in decades," Starmer said at a joint press conference following his meeting with the Japanese prime minister.

Starmer's visit to Japan was his first since taking office in July 2024. He is also the first British prime minister to visit Japan since Rishi Sunak's trip in May 2023 for the G7 summit in Hiroshima. Excluding visits tied to multilateral meetings, this is the first since Theresa May's visit in August 2017.

His visit to Japan drew particular attention in both Japan and the United Kingdom, given that it followed a three-night, four-day visit to China.

China Backlash and the Japan Signal

The UK's opposition Conservative Party and China hardliners have strongly criticized Starmer for visiting Beijing to strengthen trade and investment ties as part of efforts to revive Britain's stagnant economy. 

Critics argue that the move amounts to "aiding an enemy," accusing him of tacitly accepting Beijing's suppression of the pro democracy movement in Hong Kong, human rights abuses in the Xinjiang Uyghur Autonomous Region, and Chinese espionage activities in the UK.

Many Japanese and British experts interpreted the one-day visit to Japan, which appeared to have been added to Starmer's China trip, as an effort to balance out the criticism back home. 

At the same time, Starmer signaled the importance he places on Japan by inviting Prime Minister Takaichi to Chequers. The invitation to the British prime minister's official country residence outside London is regarded as a high level of hospitality in British diplomatic practice.

From Assurances to Action

On February 2, Starmer was asked in the House of Commons whether engagement with China would undermine Britain's partnership with Japan, which the questioner described as one of the country's most important democratic allies. Starmer replied simply, "I can promise that."

That said, Japan and the United Kingdom have steadily deepened their relationship in recent years, particularly in the security and economic domains.

Following its departure from the European Union in 2020, widely known as Brexit, the United Kingdom moved to strengthen its trade ties with the Indo-Pacific region, including Japan. 

In 2021, Japan and the UK brought a Comprehensive Economic Partnership Agreement into force, expanding bilateral trade to more than £33 billion (about $45 billion USD) annually. 

Moreover, Britain joined the Japan-led Comprehensive and Progressive Agreement for Trans Pacific Partnership in 2024. And in 2025, the two sides held the inaugural meeting of the Economic Policy Consultative Committee, the economic counterpart to the 2+2 framework.

In the security field, the two have increasingly worked to improve interoperability. In 2017, the two countries implemented the Acquisition and Cross-Servicing Agreement, allowing the Self-Defense Forces and the British Armed Forces to exchange supplies and services. 

This was followed in 2023 by the Reciprocal Access Agreement, which simplifies procedures for reciprocal visits during joint training exercises.

Deterrence, With Limits

In 2025, the United Kingdom deployed an aircraft carrier strike group led by HMS Prince of Wales to the Indo-Pacific for more than six months. The carrier called at ports in Japan in August and September. It was the first visit by a British aircraft carrier in four years, following HMS Queen Elizabeth’s port call in 2021.

The British government has defined renewed engagement with the European Union and expanded involvement in the Indo-Pacific as the two pillars of "Britain's renewal."

In that sense, strategic stability in the Indo-Pacific is also a key concern.

It is unrealistic to expect the United Kingdom to immediately dispatch an aircraft carrier strike group in support of Japan, the United States, and Taiwan in the event of a Taiwan contingency. 

Yet Britain's decision to deploy carriers to the Indo-Pacific during peacetime carries strategic weight. As a member of the free and democratic camp, the UK's visible presence complicates Beijing's calculations and strengthens deterrence against attempts to unilaterally alter the regional status quo.

Even so, the Japan-UK security partnership carries unresolved uncertainties. The Global Combat Air Programme, a joint sixth-generation fighter project involving Japan, the United Kingdom, and Italy, was expected to move forward with the signing of a development contract late last year. 

Largely due to domestic circumstances in the UK, however, the agreement remains unfinalized.

Strategy Meets Fiscal Reality

The UK had planned to unveil a Defense Investment Plan last autumn to strengthen its military capabilities in response to threats such as Russia. Under the plan, the country sought to build nuclear submarines, develop nuclear warheads, and participate in the Global Combat Air Programme.

But when projected costs were fully calculated, a budget shortfall of £28 billion (about $38 billion) by 2030 came to light. London has pledged to raise defense spending to 3.5% of gross domestic product by 2035, but even that increase appears insufficient to cover the planned expenditures. 

The Ministry of Defense has been forced to reassess its investment priorities, fueling growing uncertainty over the future of the GCAP.

Responding to questions in the House of Commons on February 2, Starmer described the GCAP as "a very important plan" and said he intended to push it forward. 

Yet he stopped short of offering specifics, saying only that the Defense Investment Plan would be "announced soon."

GCAP Delays and Allied Unease

A US military official told The Sankei Shimbun that the GCAP is already falling behind the United States' sixth-generation F-47 fighter program, citing delays caused by budgetary constraints in the United Kingdom.

The US official further noted that a more realistic path would be to explore a cooperative framework among Japan, the United Kingdom, and the United States, a so-called "JUAKUS" arrangement.

Such a framework would build on longstanding security cooperation and deep military trust with the United States, following the model of the US-UK-Australia AUKUS partnership for nuclear submarine development.

The official's comments appear to reflect a growing sense of alarm within parts of the American security community. At issue is a widening gap between Japan and the UK, long regarded as pillars of US global strategy, and the Donald Trump administration that prioritizes the Western Hemisphere under the banner of "America First."

In practical terms, Japan and the UK are unlikely to distance themselves from the US on their own. Both countries place their alliances with Washington at the core of their foreign and security policies.

Simultaneously, though, the Trump administration has repeatedly taken actions that some see as undermining the international order built under US leadership after World War II. 

Japan and the UK, as America's two closest allies, are expected to act as a stabilizing force. 

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Author: Yoshinari Kurose, The Sankei Shimbun 

(Read this in Japanese)