A wave of alarm is sweeping through the United Kingdom after unredacted blueprints revealed that China plans to build a hidden underground room inside its new London super embassy directly beside some of the most sensitive communication cables in the country. The site is located on the former Royal Mint near the City of London, an area that handles enormous volumes of financial and internet traffic every second.
These fiber optic cables are part of the London Internet Exchange, one of the largest digital hubs on Earth. They carry bank transactions, salary payments, emails, instant messages, and data for millions of people. They also connect London to undersea cables that link Britain to the United States. Whoever can access these lines can see the flow of modern economic life. That is why security experts say the location of this secret room is not a coincidence.
A Hidden Chamber Built Next to the Cables
The unredacted plans show a triangular underground chamber measuring up to 40 meters across and two to three meters deep. It sits directly under the north west corner of the embassy site along Mansell Street. The outer basement wall is set to be demolished and rebuilt, which will place Chinese construction crews and later Chinese officials just over one meter from the buried fiber optic cables.
Those cables belong to major companies such as BT Openreach, Colt Technologies, and Verizon Business. They connect the financial centers of London to large data centers in Docklands and beyond. Together they form the core of the London Internet Exchange, which handles vast volumes of data from banking, trading, email, and online communications.
Professor Alan Woodward of the University of Surrey said the layout alone raises serious questions. He explained that China has not said what the basement room will be used for, but that the design leaves little room for comfort. He said, “It could be legitimate classified communications equipment but that can hide a multitude of sins.”
Cooling Systems That Point to High Powered Computers
What truly alarms experts is what the blueprints show inside the hidden room. At least two hot air extraction systems are built into the design, venting heat through a lightwell and a new grille. That kind of ventilation is usually needed to cool high powered computers and large banks of servers.
Security specialists say this suggests that the room is meant to host serious computing equipment. Professor Woodward said, “If they wanted to tap the cables they would not need to go far. You would not know what was happening down there.”
He also warned that the demolition and rebuilding of the basement wall right next to the cables is a red flag. He said, “There is a long history of cable tapping by East and West alike. Anyone who can do it has done it.”
The Target
The cables running beneath Mansell Street carry financial transaction data used by banks to process deposits, withdrawals, and payments. They also carry messages, emails, and internet traffic for businesses and private citizens. These lines link data centers across London and connect to transatlantic cables that reach the United States.
Professor Woodward stressed that modern espionage is not only about state secrets. “Economic intelligence is central to the mission of foreign intelligence services,” he said. “If I were in their shoes, having those cables on my doorstep would be an enormous temptation.”
Even small leaks from fiber optic cables can be read by specialized equipment if the cables are bent or tapped in the right way. Devices can also be placed directly on top of the lines to siphon off data without anyone knowing. The technology for this is not new.
Most of the embassy plans were heavily redacted when submitted to local authorities. China said the missing sections were removed for security reasons. That secrecy led to years of suspicion and delays.
The full picture only came out because The Telegraph obtained the unredacted documents and published them. The release came just days before Prime Minister Keir Starmer is expected to approve the project ahead of a visit to China where he will meet President Xi Jinping.
The plans show not just one secret room but a network of 208 hidden rooms beneath the embassy complex. These include power rooms, communications ducts, sprinkler systems, lift shafts, tunnels, and areas that could house people and equipment underground for long periods.
A Facility Designed for Long Term Operations
The blueprints reveal emergency generators, high voltage electricity rooms, water supply systems, and telecoms connections. There are tunnels linking different parts of the site, including a tunnel connecting the Seamen’s Registry building to a large underground car park.
There are also toilets and showers in the basement, which means staff could remain underground for extended periods. Adjacent rooms vary in size, with some large enough for a gym and others small and secure behind winding corridors and multiple doors.
Above ground, the plans show flats for senior diplomats and studio style units for staff. Together, the design looks more like a self contained technical and intelligence campus than a normal embassy.
Alicia Kearns, the shadow national security minister, said approving the embassy would hand China a powerful strategic advantage. She called it “a launchpad for economic warfare at the very heart of the central nervous system of our critical financial national infrastructure.”
She added that the unredacted plans show a concealed room running immediately alongside the cables that serve the City of London and Canary Wharf. She said the threats are obvious and asked why the government would ignore them.
Professor Anthony Glees, a professor of intelligence and security at the University of Buckingham, said it would be “absolutely mad” to allow the project to go ahead. He said, “You can see from the plans how close rooms run to those cables. They can be tapped very easily.”
He also pointed to the heating systems in the secret room, saying they are suitable for large servers. In his view, the site would not just spy on the United Kingdom but would become “the Chinese intelligence hub for the whole of Europe.”
The British government says national security has been taken seriously throughout the planning process. A government spokesman said, “National security is our first duty and government security experts have been involved throughout the process so far.”
Officials also say the cables do not carry sensitive government data. But critics argue that financial and commercial data is just as valuable to a foreign intelligence service.
BT Openreach said it has strong security measures in place and works with the government to protect its infrastructure. China’s London embassy did not respond to requests for comment.
ACZ Editor: This is old hat planning for an embassy to try to put itself in the position to spy as much as possible. The solution to the cable problem is actually very simple. You simply make room around the cables to allow frequent inspection. Of you can simply (and expensively) move the cables.