Well, possibly. Data centres are the cotton mills and steel 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.

One of DC01UK's visualisations of their proposed data centre in South Mimms, Hertfordshire. — One of those visualisations that developers churn out. More here.

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 developer applied for planning permission in September of last year and last week the council granted outline permission for the development. We suspect they’re as excited as we are, although there’s some doubt as to how involved Hertsmere can now be, given the special status of this development. We’ll be keeping an eye on this project and we’ll provide as much detail as we can as it progresses but, to begin with, here’s what we know so far:

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 recently been calling ‘grey belt‘. You might expect a plan to build on 85 acres of agricultural land in a district that has a history of green belt belligerence 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.

Map showing the area to the East of South Mimms services in Hertsfordshire, between Potters Bar and the M25 motorway. Marked on the map is the proposed site of a large data centre. — Inside the red outline

It’s going to be huge. The claim, in the news stories and press releases, that DC01UK will be the largest data centre in Europe looks narrowly defensible – but we’d be surprised if it’s still the case once it’s actually finished. 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 – although it will be built in phases. 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. And as we’ll explain, there are other important numbers – relating to water and electricity use and to pollution – that we should understand and keep an eye on.

But size isn’t everything. If completed (big question!) – 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 brutal and connected directly to the financial performance of the companies that use these facilities. Data centre capacity is a commodity – like bauxite or wheat. The biggest firms (Google, Amazon…) build and run their own but most data centre capacity is bought and sold by intermediaries or brokers. A business that needs servers for a new app is concerned only with cost; margins must be hair-thin, effiency constantly improving. So, honestly, how this plays out, between now and the proposed opening date in 2030 is anybody’s guess. Whatever happens, as you’d expect, this enormous facility is already well-and-truly 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 (truly visible from space). Also, 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.

A visualisation of a data centre proposed for land near South Mimms in Hertsmere, UK. A modern, two-story industrial building is surrounding by planting. — Another one of those visualisations.

Who will own the data centre? Guess what: we don’t know. We know a bit about the company set up to see it through planning, DC01UK, but nothing about the facility’s final user nor even its ultimate owner. This project is, according to Computer Weekly, a joint venture with local house-builder Griggs and Chiltern Green Energy, neither of which – I hope they won’t mind me saying – are what you’d call giants of the information age. The Register, a UK tech news web site, says it will ultimately be used by one of the ‘hyperscalers’ (industry jargon 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. This is not surprising. The big firms are typically secretive about their data centres: these are, to state the obvious, business-critical, round-the-clock facilities and ‘uptime‘ must be protected at all costs. Amazon, in particular, treats its data centres as if they were national security assets and

DC01UK: Hertsmere steps into history