Two gigawatts under the sea: Britain plans a major upgrade to its transmission grid

The United Kingdom has approved the construction of a subsea power cable with a transmission capacity of 2 gigawatts, connecting Suffolk in eastern England with Kent in the southeast of the country, the British government announced on Friday. The 138-kilometre link, called Sea Link, is expected to begin construction early next year.

According to the UK Department for Energy Security and Net Zero, the project will strengthen the country’s energy security, increase the resilience of the electricity grid and reduce power transmission losses, helping to lower costs. The project is being developed by National Grid. The subsea cable will be manufactured by Japan’s Sumitomo Electric at its factory at the Port of Nigg in Scotland, whose construction required an investment of 350 million pounds.

Construction is expected to begin in early 2027. The project is scheduled for completion in the 2030s, with the timeline dependent on more detailed planning and the signing of construction contracts. According to the UK’s transmission system operator, the National Energy System Operator, the country will need to invest around 89 billion pounds in grid modernisation by the 2030s. The investment is intended to help renew ageing infrastructure, meet expected growth in demand and connect more renewable energy sources.

The announcement on the government’s website links the project to the recent approval of two large solar farms. As an island nation, Britain has extensive experience with subsea cables. In addition to international interconnectors and connections linking offshore wind farms to the grid, it also uses them to connect some islands.

Interconnectors

The new cable between Suffolk and Kent should be distinguished from international subsea links, known as interconnectors. These allow the United Kingdom to trade electricity with neighbouring countries. The British transmission system currently has ten operational interconnectors with a total capacity of 10.3 GW, linking the country with France, Belgium, the Netherlands, Norway, Denmark, Ireland and Northern Ireland. Another connection with Germany, with a transmission capacity of 1.4 GW, is under construction.

Electricity can flow through these cables in either direction, depending on supply, demand and prices in each market. This allows Britain to import electricity when domestic generation is insufficient or more expensive, and conversely to export surplus power, for example when wind generation is high.

In the 12 months to September 2025, the United Kingdom imported 43 TWh of electricity, equivalent to around 13% of its gross consumption, while also exporting 12 TWh. The British government aims to increase cross-border interconnector capacity to 12–14 GW by 2030.