Every large data centre in Britain depends on one thing before anything else: a connection to the electricity grid. In 2026 that connection has become the hardest part of any project to secure. Hundreds of gigawatts of proposed generation and demand are queued for a connection, and the wait reshaped how data centres are planned, valued and financed across the country. The response, a connection reform led by the National Energy System Operator, is now reordering that queue.
This guide explains what the connection queue is, how it grew so large, who runs it, and how the reform known as TMO4+ changes the rules. It closes with what the new system means for data centre developers, buyers and lenders, and how to read the queue as a signal.
What is the grid connection queue?
Any project that wants to connect a large load or a new generator to the transmission network, from a wind farm to a data centre, has to apply for a connection agreement that sets out where, how and when it can connect. For years those applications were processed first come, first served. A project joined the back of a single queue and waited its turn, regardless of whether it was ready to build or whether the network had room. As applications piled up, the queue became the gatekeeper for the whole system.
How big is the queue, and why?
By early 2025 the volume of projects waiting for a transmission connection in Great Britain had passed 750 gigawatts, around four times the generation the country needs to meet its 2030 clean power target. Most of that volume is generation rather than demand, but the effect on data centres is the same. The queue grew because applying was cheap and easy, so speculative and stalled projects accumulated alongside real ones, clogging the process. Many held early queue positions without firm financing, land or planning, while genuinely ready projects waited behind them. The system was sorting by application date, not by readiness or need.
Who runs the queue?
Responsibility sits with the National Energy System Operator, known as NESO, which took over from the National Grid Electricity System Operator in 2024 as Great Britain's independent system operator. NESO plans the network, manages connections and runs the reform of the queue, working with the regulator Ofgem and the network owners. Its independence from any network or generation business is meant to let it prioritise the system as a whole.
What is the TMO4+ reform?
NESO's reform package, known as TMO4+, replaced first come, first served. It went live on 10 June 2025 after Ofgem approved it in April 2025. The reform sorts projects into two gates. A firm Gate 2 queue is for schemes that are ready and needed, with the land, financing and strategic fit to proceed, and these receive firm connection dates. An indicative Gate 1 waiting list holds the rest until they can demonstrate readiness. The governing principle is first ready, first needed, first connected. Projects must meet readiness criteria and align with the strategic plan for the network to move into the firm queue, which is meant to clear out speculative applications and let viable projects connect sooner.
What it means for data centres
For data centres the change is direct. A connection date no longer depends on when an application was filed but on how ready and how needed a project is. That rewards developers who have secured land, capital and planning, and penalises those holding speculative positions. It also means a data centre can no longer treat a grid connection as a formality confirmed late in the process. The connection is now the first question, and a credible energisation date is the difference between a deliverable site and a stranded one.
What it means for buyers, developers and lenders
The queue reform changed how data centre assets are valued. A site with planning consent but a connection date late in the decade is a very different asset from one with firm capacity in the next two or three years, even if the two look identical on a map. Buyers now underwrite the connection, not just the building. Lenders ask for the connection agreement and its gate status before committing. Developers chase powered land, brownfield sites with existing supply, and regions where the network has genuine headroom, because that is what turns a scheme into something a buyer can finance. Across the market, the connection has moved from a detail to the central fact in any transaction.
How to read the queue
Because the connection now decides feasibility, the queue is one of the clearest public signals of where capacity is genuinely heading. Connection applications and gate positions held by NESO show where large loads are seeking power and which projects have moved into the firm queue. Read alongside council planning filings and water referrals, they reveal which sites are real and which are marketing, often years before any announcement. For anyone buying, financing or developing capacity, tracking the queue is no longer optional.
Frequently asked questions
How big is the UK grid connection queue?
By early 2025 the volume of projects waiting for a transmission connection in Great Britain had passed 750 gigawatts, around four times the generation the country needs for its 2030 clean power target. Most of that is generation rather than demand.
What is TMO4+?
It is NESO's connection reform, live since 10 June 2025 after Ofgem approval in April 2025. It replaced first come, first served with a two-gate system that prioritises projects which are ready and needed, under the principle first ready, first needed, first connected.
Who runs the UK grid connection queue?
The National Energy System Operator, or NESO, which became Great Britain's independent system operator in 2024, taking over from the National Grid Electricity System Operator. It manages connections and the queue reform with the regulator Ofgem.
Why does the queue matter for data centres?
Because a data centre cannot run without a grid connection, and securing a firm connection date is now the hardest part of any project. A site can hold land, planning and funding yet still wait years for power, so the connection decides feasibility and value.
How does the reform help data centres connect faster?
By clearing speculative and stalled projects out of the firm queue and prioritising schemes that are ready and needed, the reform aims to free capacity and shorten timelines for viable projects, including data centres that can demonstrate readiness.