Well, possibly. Data centres are the cotton mills and foundries of our day. Vast, industrial-scale facilities that are right at the heart of the fourth industrial revolution. And one might be built right here, next to the motorway in South Mimms.

We’ll admit to a certain childish excitement about this. Mysterious developers want to build Europe’s largest data centre right here in Hertsmere. The council has granted ‘outline permission’ for the development so there’s already some progress. We suspect they’re as excited as we are. We’ll try to keep an eye on this project and to provide as much detail as we can as it progresses but, to begin with, here’s a quick tour of what we know so far (and what might bring it to a grinding halt).

Are you serious? On the green belt? The data centre, if built, will be on green belt land to the East of South Mimms services, right next to the M25. The developers are in luck, though: this is exactly the kind of relatively-unloved green belt that the government has in mind when they say ‘grey belt‘. You might expect a plan to build over 85 acres of agricultural land in a district that has a history of successfully protecting the green belt (and an uninterrupted history of Conservative representation in Parliament) to produce an angry reaction (like the one that held up the Radlett Railfreight terminal for years) but when even Peter Waine, chair of the Hertfordshire branch of the Campaign to Protect Rural England, speaking to the BBC, can’t muster more than: “It may not be the most wonderful and beautiful green belt but it is green belt…” Here at Radlett Wire, at the other end of Hertsmere, we get the strong feeling this particular chunk of green belt may not be long for this world.

Size isn’t everything. The claim, in the news stories and press releases, that DC01UK will be the largest data centre in Europe looks defensible. Europe’s largest running data centre is presently in Portugal. It covers about 800,000 square feet and the proposed South Mimms operation is aiming for two million square feet. But there’s another project, in Newport, Wales, that’s also aiming for two million and, anyway, the critical measurement – especially for the local community – is probably not square feet. Planners and architects use a measure they call gross external area (GEA), which is more useful. It’s the total area of a building, including all floors, measured from the outside. It’s the critical measurement used for rating, council tax and planning. DC01UK’s GEA is 187,000 square metres, slightly more than the 185,000 square metres (2,000,000 square feet) that will be devoted to computers.

Okay, size is everything. If completed – and if not eclipsed by other projects along the way – this puts DC01UK just inside the top ten biggest data centres in the world, but it’s an extremely volatile market and connected very directly to the financial performance of the companies that use these facilities – so honestly, a lot of this is really anybody’s guess. Either way, as you’d expect, this enormous facility is still going to be dwarfed by the biggest. A single Chinese data centre, operated by China Telecom, is already over five times bigger than DC01UK and sits on a campus called the Inner Mongolia Information Park in Hohhot, China alongside several other enormous facilities. You probably won’t be surprised to learn that the seventh largest data centre in the world is buried in the side of a mountain in Utah and is operated by the United States National Security Agency. It’s safe to say that, although you’ve never heard of it, it knows a fair amount about you.

Who owns it? Guess what: we don’t know. The company set up to see it through planning, DC01UK, won’t be the facility’s final user nor even its owner. The Register, a reliable UK tech news web site, says it will ultimately be used by a ‘hyperscaler’ (the industry term for the handful of tech giants in a position to make use of such a huge facility) but that the usual suspects – Amazon, Google, Microsoft and Meta – all declined to comment. There’s only one project described on DC01UK’s web site and there’s no ‘about us’ page. The firm was incorporated in 2022 and was originally called Hilfield Battery Storage so we assume it’s connected with the failed application to build a battery storage farm on Hilfield Farm in Aldenham, rejected last year after a public inquiry. We don’t know enough about any of the firms involved here but we suspect there will be people in Hertsmere who’ve done their research – we’d love to hear from you in the comments!

So why all the excitement? Data centres have been a big deal for a long time, since the first of the really huge online businesses began to build their own all around the world. But the pressure to provide new data centre capacity has recently multiplied – and it’s become a very big story in the business and technology press and on social media – and it’s all because of artificial intelligence (AI). It’s a complicated story but, to keep it short, AI needs an enormous amount of computing power – both in training new models and in running queries against them once they’re live. Typing a query into ChatGPT will usually use at least ten times more computing power – and thus electricity – than a Google search. And the industry really didn’t see this coming. It’s less than two years since it dawned on the tech firms and on their investors that they were going to need many times more computing power than previously projected. So the rush is on. Governments and local authorities everywhere have noticed this massive new opportunity and are rushing at it. Three weeks ago Keir Starmer launched his AI action plan, which he says will ‘deliver a decade of national renewal’. We should probably also acknowledge the boldness of Hertsmere here. Council leader (and head of something called the Hertfordshire Growth Board) Jeremy Newmark has obviously pushed this along very quickly. Apart from the obvious explosive dynamism of the AI industry he’ll be aware that, here in Britain, the government has committed to a completely new and much more aggressive orientation on economic growth – and to change planning procedures to speed up development. More specifically, data centres have been reclassified as critical national infrastructure and will have special status when it comes to planning. There’s a decent chance that this project will be fast-tracked to approval.

But could anything hold it up? Short answer: yes. And it won’t just be planning. Even in the couple of weeks since we first learnt about the project, the terms of the explosion in data centre capacity have changed completely. Less than a week before Hertsmere’s DC01UK announcement a new Chinese-built AI model called Deepseek R1 was launched. To say that it caused an epic freak-out at every level of the AI ecology would not be an overstatement. The freak-out centred on the fact that this new software was almost as efficient as the leading American models although it had been built on simpler technology – and much more cheaply. It was a huge shock, challenging the fundamentals of the emerging industry. As it dawned on the company’s competitors that a rich and useful AI model could be built using a fraction of the resources, that their assumptions about the progress of the technology could be all wrong, share prices tumbled, projects were cancelled or paused, projections and forecasts altered. So, could this global chaos change the trajectory of the South Mimms project? Cause it to be cancelled or scaled back? It really could. At Hertsmere everyone will have their fingers crossed.

In the next post, more about the crazy business of powering (and cooling) a modern data centre.

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• For comparison, the largest warehouse in the UK – belonging to Amazon.com, natch – also covers around two million square feet. The O2 covers 1,126,270 square feet.
• The story of the data centre goes back even before the web and the explosion of online business. In earlier lives we were lucky enough to visit a sophisticated data centre built for BT in London Docklands almost forty years ago.
• Bookmark this page to keep up with our updates on DC01UK. If you’re one of those weirdos who still usea an RSS reader, follow this feed.