A team of researchers has just pushed data through an optical fibre buried beneath London faster than anyone had managed before, using cabling that was already in the ground. The headline figure is 450 terabits per second, a new world record for this kind of link. It sounds abstract, but the experiment says something concrete about where home broadband is heading over the next decade.
A record set on fibre already under London
The demonstration ran along a 39 km loop connecting University College London to the Telehouse North data centre in the capital. Crucially, the cable was not a pristine strand spun for the lab. It came from the UK National Dark Fibre Facility, which means the team used ordinary, already-installed fibre of the sort that criss-crosses British cities. The work was led by Japan's NICT alongside UCL, Aston University, the University of Bristol and Nokia Bell Labs.
That detail is what sets this apart from earlier milestones. The previous records of 402 and 430 terabits per second, set in 2024 and 2025, relied on special fibre in controlled conditions. This time the team hit a higher number on real infrastructure, which is a far better guide to what the cabling already under our feet can eventually carry.
What 450 terabits per second actually means
To reach that speed, the researchers lit up five separate bands of the fibre at once and sent 1,273 wavelength channels down a single strand, using a record 42.4 terahertz of bandwidth. Today's commercial networks only tap a slice of that range.
Put plainly, 450 terabits per second is enough to move well over two thousand 4K films every single second down one hair-thin strand of glass. The researchers offer another way to picture it: a single fibre carrying that load could serve the equivalent of roughly 56,000 top-tier home connections at the same time.
Why your home connection is nowhere near this
Before anyone feels short-changed by their router, this is a research result, not a product you can order. The fastest full-fibre (FTTP) packages sold to UK homes today top out at a couple of gigabits per second, and most households sit well below even that. The record is millions of times quicker than a typical broadband line.
The gap is not a failure. A home does not need terabits; the point of this research is the backbone, not the front door. The internet's motorways, the long-haul links between cities and data centres, are what carry everyone's streaming, video calls and cloud backups at once. Proving that buried fibre can hold this much traffic means those motorways can grow without digging up the streets again.
What it could mean for full-fibre at home
The practical promise is headroom. As more of the country moves onto full-fibre and demand keeps climbing, the same cables already in the ground can be pushed much further simply by upgrading the kit at each end. That is cheaper and faster than laying new lines, and it is exactly the kind of advance that keeps speeds rising and prices in check.
For now, the sensible move is to make the most of what is actually available on your street. If you are still on part-fibre or an ageing copper line, comparing full-fibre broadband deals is the single biggest jump most homes can make today.