In 2022, network operators flagged that parts of West London had little spare electricity capacity for major new connections. That warning reshaped where data centres get built across the South East, and its effects are still working through the market in 2026.
What happened in West London?
In summer 2022 the Greater London Authority became aware that three boroughs, Ealing, Hillingdon and Hounslow, had effectively run out of distribution headroom for large new loads. The Mayor wrote to government in July 2022 to raise the alarm. Developers were told that major applications needing more than one megavolt ampere of supply could face waits of several years, with some connection dates quoted as far out as 2035. There was no formal ban on building, but for any power hungry use the practical effect was close to one.
Why did the capacity run out?
Several pressures arrived at once. Demand for electricity in the area had been rising for years through the electrification of heat and transport and a steady pipeline of new homes. At the same time, large concentrated loads were connecting to the same network. The GLA pointed to data centres, which had clustered in West London because of the fibre routes running along the M4, and noted that they draw power on the scale of a town or small city. With the distribution and transmission network already near its limit, there was little headroom left for anyone.
The deeper problem was timing. New transmission and substation capacity takes years to plan, consent and build, while demand from data centres, housing and electrification climbed far faster. Once the existing headroom was committed, there was no quick way to add more, so connection dates were pushed out rather than refused outright. That mismatch between fast rising demand and slow network build is the root cause that still shapes the South East market.
Were data centres to blame?
The picture is more mixed than the early headlines suggested. The data centre sector pushed back on being singled out, pointing out that housing, commercial demand and electrification were all competing for the same constrained network, and that operators had connected through proper processes. What is fair to say is that data centres are unusually large and concentrated loads, so a handful of sites can account for a substantial share of an area's spare capacity. The honest conclusion is that West London ran into a network that had not kept pace with total demand, and data centres were one significant part of that demand rather than the sole cause.
What is being done about it?
City Hall convened Scottish and Southern Electricity Networks and National Grid to find short and longer term fixes. SSEN ran a capacity allocation study that found headroom for stalled housing, releasing power for several thousand permitted homes by March 2024, with City Hall later reporting more than 11,000 permitted homes freed in total. Network operators have also looked at demand flexibility and targeted reinforcement. At the national level, NESO's TMO4+ connection reform, live since June 2025, is reordering the wider queue so that ready and needed projects connect sooner. None of this creates large new headroom overnight, but it changes how the remaining capacity is allocated.
Where the displaced demand is going
Developers responded the way they always do when a market tightens. They secured powered land further out and in other regions. Demand has moved to sites around the wider M4 corridor and Berkshire beyond Slough, to Hertfordshire around Hemel Hempstead, and increasingly out of the South East altogether. South Wales has drawn large projects to Cardiff, the North is growing through Manchester, and the government's first AI Growth Zone at Culham in Oxfordshire offers power and faster planning for very large new campuses. The common thread is simple. Capacity is forming where power can actually be delivered.
What it means for buyers, developers and lenders
The practical lesson of West London is that a site is worth what its power makes it worth. A plot 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 date before committing. Developers chase powered land, brownfield sites with existing supply, and locations where the network has genuine headroom, because that is what turns a scheme into something deliverable. The squeeze made power the first question in any transaction rather than a detail confirmed late in diligence.
How to read where it re-forms
The clearest way to see where displaced demand is landing is to track the public record. Grid connection queue positions held by NESO show where large loads are seeking power. Council planning applications, followed through services such as Planit, show where sites are being designed and consented. Together they reveal the next clusters well before they are announced or built, which matters for anyone buying, selling or financing capacity.
Frequently asked questions
Is there a data centre moratorium in West London?
There is no formal ban, but from 2022 major new connections above one megavolt ampere in parts of West London faced multi year waits, with some dates quoted as far out as 2035. In practice that stopped most large new power hungry developments in the affected boroughs.
Which boroughs were affected?
The Greater London Authority identified Ealing, Hillingdon and Hounslow as the boroughs short of electricity capacity for major new connections.
Did data centres cause West London's housing delays?
They were part of it, not the whole story. Data centres are large concentrated loads and absorbed real headroom, but housing, commercial demand and the electrification of heat and transport were all competing for a network that had not kept pace with overall demand.
When will West London's grid capacity improve?
Some headroom has already been freed for housing through capacity studies and targeted measures, and national connection reform is reordering the queue. Large scale relief depends on longer term network reinforcement, so the constraint on very large new loads is easing gradually rather than all at once.
Where are operators building instead?
They are securing powered land further out along the M4 corridor and in Hertfordshire, and increasingly in South Wales, around Manchester, and in designated AI Growth Zones such as Culham, where power is more readily available.