Greater London Authority to Prioritize 'Clean, Green and Efficient' Data Centers, Eyes Grey Belt Sites in Draft London Plan

The Greater London Authority (GLA) has signaled a strategic shift in how it will approach future data center development, vowing to prioritize facilities that are "clean, green and efficient" while simultaneously opening the door to construction on the city's grey belt land. The policy direction comes as part of the latest iteration of the London Plan, the capital's statutory development blueprint, which was released for public consultation in July and will remain open for feedback until October 2026.

The draft plan, which is refreshed every five years and is slated for public examination next year before formal adoption in early 2028, dedicates an entire section to the data center industry, explicitly labeling it an "industry of the future" and incorporating it into the city's key performance indicators. According to the Mayor of London's website, this marks a notable elevation of the sector's importance within the city's long-term planning framework.

Under the proposed criteria, a "suitable location" for a data center must be assessed against a range of factors, including the availability of electricity and water supply, proximity to existing data center clusters, opportunities for heat recovery, and potential conflicts with housing, employment, or infrastructure needs. Air quality impacts are also to be weighed in the evaluation process. However, the plan introduces a significant caveat: where no suitable locations can be identified, authorities are directed to explore sites "in the grey belt or on the edge of BLGs (Broad Locations of Growth) in the Green Belt." BLG is a new designation introduced in this draft, referring to areas earmarked for mixed-use or industrial development.

The concept of grey belt has become a contentious issue in UK planning policy. Introduced by the Labour government in December 2024 as an amendment to the National Planning Policy Framework, grey belt refers to Green Belt land that has previously been developed—essentially brownfield sites—or land that does not "strongly contribute" to the Green Belt's core purposes, such as preventing urban sprawl or preserving the character of historic towns. Critics argue that the definition is too vague and permissive, potentially opening the door to industrial development, including data centers, on protected land.

The debate is not merely theoretical. In June 2026, the UK government approved a 147MW data center proposal in Slough, a decision that was "called in" by then-Secretary of State Steve Reed. The intervention came after developer Tritax argued that the 74-acre site, known as Manor Farm and comprising both greenfield and brownfield land, should be classified as grey belt rather than Green Belt. The approval has since become a touchstone for how the grey belt designation might be applied in practice.

The draft London Plan also addresses operational aspects of data center design, offering guidance on cooling systems and the testing of backup generators. Notably, it suggests that the proportion of data center developments achieving a Power Usage Effectiveness (PUE) of 1.1 could serve as a measurable indicator of the plan's success. PUE is a widely used metric that assesses the energy efficiency of a data center, with a lower value indicating higher efficiency.

"London is home to Europe's largest data center cluster," the draft plan states. "They support the growth of important data-driven sectors and AI. But this growth will only deliver real benefits for London if the infrastructure that enables it is clean, efficient and aligned with the Mayor's climate goals." That sentiment echoes earlier remarks by Mayor of London Sadiq Khan, who has made clear that his support for the sector is conditional. "My ambition is clear, I want London to become the world's leading city for environmentally friendly, low-emission, high-efficiency data center development, and AI infrastructure so that our capital remains a leading global hub for digital innovation," Khan said in June, as part of a broader pledge to manage the impacts of data centers on the city.

Industry observers note that the plan's dual emphasis on sustainability and land-use flexibility reflects a broader tension across the UK and Europe, where surging demand for digital infrastructure is colliding with strict environmental and planning regulations. By setting explicit criteria for location and efficiency, the GLA appears to be attempting to strike a balance between fostering economic growth and meeting climate commitments. The final version of the plan, expected to be adopted in 2028, will be closely watched by developers, investors, and local communities alike.