Photo by Owen Wei

The UK and Japan have agreed a landmark Offshore Wind Compact worth up to £9 billion, unlocking Japanese investment into floating offshore wind projects and cementing the UK’s position as Japan’s leading clean energy partner in Europe. The agreement was signed by Prime Ministers Keir Starmer and Sanae Takaichi at Downing Street on 13 June, ahead of the G7 summit in Évian-les-Bains, as part of a broader £18 billion UK-Japan investment package spanning energy, infrastructure, financial services and technology.

The offshore wind compact, developed in close partnership with Great British Energy, will support the development of 5.9GW of floating offshore wind capacity in the UK across three flagship projects. When built, the government says they will collectively generate enough clean electricity to power 8 million homes.

PM Starmer said: “These landmark agreements will bring multibillion pound investment into the UK, creating tens of thousands of new jobs and driving new developments. As G7 economies and close security partners, we are working together with Japan on some of the most innovative technology in the world, harnessing the best of British and Japanese research and industry to deliver growth and security to every corner of the United Kingdom.” He described the talks with Takaichi as “very productive.” Speaking through a translator, Japan’s prime minister said the UK is “an extremely important partner.”

The three projects

The compact centres on three floating wind projects, all of which already carry Japanese connections. Ossian, the largest at a planned capacity of 3.6GW and located around 84km off Scotland’s east coast, is owned by Copenhagen Infrastructure Partners, SSE and Marubeni Corp, one of Japan’s largest trading houses. Green Volt, a 560MW project 80km from Scotland’s east coast, is owned by Flotation Energy, a Scotland-based subsidiary of Tokyo Electric Power, and Norwegian firm Vårgrønn. It secured a contract for difference from the UK Government in 2024 and is set for commissioning in 2029. The third project, Erebus, is a 100MW demonstration scheme in the Celtic Sea owned by Blue Gem Wind, a joint venture of Simply Blue Energy and TotalEnergies. Kansai Electric Power, the Japanese utility, acquired a majority stake in Simply Blue Energy in October 2025.

The compact therefore consolidates and formalises investment relationships that were already taking shape, while providing a framework for further Japanese capital to flow into UK floating wind more broadly.

The wider package

The offshore wind deal sits within a broader investment announcement that the BBC noted comes with the caveat that it is not clear how much represents genuinely new money rather than previously announced plans. On the infrastructure side, Japanese property developer Mitsubishi Estate committed £2 billion and Japanese insurer Dai-ichi Life £4.5 billion to building new towns, office space and innovation hubs. Hitachi Energy UK committed to creating at least 500 new jobs over the next five years, including 100 highly skilled roles at its new Glasgow Centre of Excellence and over £18 million investment in a Stafford facility.

Beyond energy and infrastructure, the two countries signed a new UK-Japan Frontier Technology Partnership, combining the UK’s software and research expertise with Japan’s hardware and manufacturing capabilities across AI, quantum computing, civil nuclear and defence. A formal partnership was also signed between the UK Semiconductor Centre and Rapidus, Japan’s advanced chip manufacturing facility, to create a direct pathway for UK-designed semiconductors to be manufactured at scale.

The leaders additionally reaffirmed their shared commitment to the Global Combat Air Programme, being developed alongside Italy, and announced a new Defence Capability and Industrial Council to foster industrial cooperation on dual-use technologies such as drones and AI. A joint declaration on economic security cooperation was also signed, covering supply chain diversification, particularly in response to concerns about export restrictions on critical minerals from China.

Energy security and the marine dimension

The government frames the compact explicitly in terms of energy security and reducing fossil fuel dependence, statingthat boosting homegrown clean energy “will help reduce reliance on volatile global fossil fuel markets, strengthen energy security, help get bills down for good.” The deal arrives at a moment when the UK economy, which grew by 0.6% in the first quarter of 2026, the fastest of any G7 economy, faces near-term headwinds, with the IMF warning the UK will be among the hardest hit by the economic fallout from the US-Israel war with Iran.

For the marine sector, the compact’s most significant dimension is the commitment to floating wind specifically. Unlike bottom-fixed offshore wind, floating technology is still at an early commercial stage and is seen as crucial to unlocking deeper water sites around the UK coastline, particularly off Scotland and in the Celtic Sea. The involvement of major Japanese utilities and trading houses at this scale provides a significant vote of confidence in the technology’s commercial viability – and in the UK’s ambitions to be a world leader in its development.