Britain’s data-cententre pipeline is running into a constraint that sits largely outside the data hall itself: access to enough electricity, in the right place, at the right time. Ofgem says demand connection applications increased from 41GW to 125GW between November 2024 and June 2025, driven largely by data centres. The regulator puts data-centre applications at at least 80GW, while around 73GW is referenced within its current reform work.
Much of the connection queue is considered speculative and Ofgem is actively trying to remove projects that are unlikely to proceed. But the scale of applications explains why grid access has moved onto the critical path for developers, MEP teams, utilities specialists and main contractors. The Government has reached a similar conclusion. Its consultation on strategic demand connections describes timely electricity connections as one of the biggest blockers to AI-capable data centres and says around 140 data-centre projects were seeking transmission connections representing approximately 50GW of capacity.
Grid connections, substations and long-lead electrical infrastructure are increasingly shaping the programme for major UK data-centre developments. Illustration: London Construction Magazine.
A 13.5GW Pipeline Does Not Mean 13.5GW Is Being Built
The difference between proposed capacity and physical construction is substantial. Savills data for 2026 puts UK live data-centre capacity at 1,803MW, with 242MW under construction. A further 2,084MW is classified as committed, while 9,371MW remains at an early stage where planning, grid access, financing or other delivery matters remain unresolved.
| Measure | Latest figure | What it means |
|---|---|---|
| Live UK capacity | 1,803MW | Operational data-centre IT capacity |
| Under construction | 242MW | Capacity physically being delivered |
| Committed | 2,084MW | More advanced pipeline, but not equivalent to completed capacity |
| Early-stage pipeline | 9,371MW | Delivery remains dependent on matters including power, planning and finance |
| Demand connection applications | 125GW total; at least 80GW data centres | Requested electrical connections, not a forecast of projects that will be built |
The numbers measure different things and should not be added together or directly compared as equivalent capacity. They do, however, show how far development ambition has moved ahead of immediately deliverable grid capacity. Savills' latest UK data-centre analysis can be viewed here, while Ofgem's current connection reform figures are set out in its July 2026 announcement.
London Still Dominates, but Power Is Moving the Boundary
London remains by far the UK's largest data-centre market. Savills records 1,637MW of live capacity in London against 1,803MW nationally, equivalent to roughly 91% of the UK total in its dataset. That concentration is also part of the problem. CBRE expects another 185MW of new London supply during 2026, following 192MW in 2025, but says expansion is moving beyond the traditional Slough and Hayes/Park Royal clusters where power availability is limited.
New campuses are being planned around Hertfordshire, Oxfordshire, Essex, North London and the Docklands. CBRE expects some of those developments to enter the market in 2028 or 2029, subject to grid availability. That makes the electricity connection more than a utilities package. It can determine the site, development phasing and commercial programme before the main data-centre building reaches construction.
Substations and Cables Are Becoming Data Centre Projects
National Grid's current construction programme shows how much infrastructure can sit beyond a data-centre boundary. Its North West London Upgrade, launched in August, includes a new 132kV gas-insulated switchgear substation at Letchmore Heath, extension of the existing 400kV Elstree GIS substation, a new 400kV cable circuit and reinforcement of the wider transmission network.
Around 60km of new cable infrastructure is planned within the existing Elstree–St John's Wood tunnel, alongside more than 200km of overhead-line upgrades. National Grid says the scheme will enable five new data centres representing about 1GW of demand. Delivery partners include Hochtief-Murphy Joint Venture, Laing O'Rourke, Siemens Energy and Hyundai Electric.
At Uxbridge Moor in Buckinghamshire, National Grid has already started construction of separate 400kV and 132kV GIS substations intended to connect more than a dozen new data centres. The connection requests associated with that location amount to around 1.8GW. Murphy is principal contractor for the substation, underground cabling and associated connection works. Those projects create work well beyond conventional data-hall shell and core: high-voltage substations, cable corridors, tunnelling interfaces, transformer bases, switchgear, protection systems, civils, commissioning and network integration.
Key Takeaway: For large data-centre schemes, practical completion of the building and availability of electrical capacity are separate programme milestones. A finished data hall without sufficient energisation cannot operate at its intended load.
Ofgem Wants Proof That Projects Can Actually Proceed
The connection queue has become large enough that regulators are now testing the commercial maturity of data-centre proposals rather than simply allocating positions in application order. Ofgem's consultation on data-centre connection reforms closed on 17 September 2026 and is currently awaiting a decision. The proposals include a Data Centre Commitment Fee for relevant large developments of between £237,500 and £712,500 per MW. The security would be held while the project progresses towards energisation and could be forfeited if it leaves the queue early.
Ofgem has also proposed project milestones requiring evidence of a credible end user, financial and technical capability and procurement of long-lead electrical equipment such as switchgear. That final requirement has a direct construction implication. Procurement of electrical plant can become part of demonstrating that the project itself is credible enough to retain scarce connection capacity. The commitment fee remains a proposal and should not yet be treated as implemented policy.
AI Growth Zones Shift Attention Beyond the M25
Government policy is also trying to steer new AI data-centre capacity towards locations where additional electricity demand can be accommodated more effectively. AI Growth Zones are intended to combine planning support with improved access to power. Government policy explicitly identifies delays obtaining electricity as one of the main barriers to AI data-centre investment.
The programme includes locations in Oxfordshire, the North East, North and South Wales and Lanarkshire. Government estimates that its package of reforms could reduce time to power by as much as five years, although that is a policy forecast rather than a delivered result. For the construction market, the geographical consequences may be more important than the headline investment announcements. The largest future campuses do not necessarily need to sit within the traditional West London cluster if suitable land, fibre and hundreds of megawatts of electricity can be secured elsewhere.
Power Procurement Is Now Part of the Construction Programme
Data-centre contractors have always dealt with substantial electrical scope. The difference is the scale at which off-site network infrastructure now affects project delivery. Transformer and switchgear procurement, grid-interface agreements, substation construction and cable routes can need to be resolved years before full campus capacity becomes operational. Developers may also phase energisation, consider flexible connections or examine behind-the-meter generation and storage where firm network capacity cannot arrive in line with the building programme.
This does not mean every UK data centre is facing a decade-long delay. Constraints vary substantially by location, and the North East, Scotland and parts of Wales present different power conditions from Slough and West London. Nor is power the only development risk. Planning, land, fibre, water, equipment lead times, finance and local environmental constraints remain relevant.
But in the established London market, there is now clear evidence that developers are looking beyond traditional clusters because secure and scalable electricity capacity is harder to obtain. CBRE's current forecasts explicitly place future delivery dates in adjacent markets against the availability of grid capacity. Ofgem's next decision on its data-centre connection proposals will therefore matter to considerably more than energy specialists. The rules will influence which schemes retain connection positions, when long-lead plant has to be committed and which parts of Britain's large data-centre pipeline can move from planning documents into physical construction.
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