China is reportedly planning to build a secret underground room that could be used to spy on the UK at the site of its controversial ‘super embassy’ in London.

Unredacted plans – unveiled on Monday night – supposedly show a hidden room in the north west corner of the building, which is just metres away from a vital cable network connecting some of the capital’s top financial sectors. 

The triangular room measures up to 40 metres across and 2-3 metres deep and includes at least two air extraction systems, according to the newspaper, seemingly indicating it could house heat-generating equipment such as high-tech computers.

It is part of a network of 208 secret rooms – a majority of which are hidden from the public in planning proposals – beneath Beijing’s ‘super-embassy’, which is set to be built on the site of the Royal Mint pending approval from Sir Keir Starmer.

Downing Street is said to have proposed that the Prime Minister approves the plans before he visits China later this month in a bid to smooth over relations with President Xi Jinping following a series of planning delays.

But there are fears the new embassy could be used as a ‘spy centre’, with some critics raising concerns that China could tap into the cables and eavesdrop on key information.

Documents unveiled by The Telegraph also reveal that the outer wall of the chamber, lying directly next to the cables, would be demolished and rebuilt, further fuelling fears they could be tapped. 

Security expert Professor Alan Woodward said this was a ‘red flag’ and having the cables so close to the building would be an ‘enormous temptation’ for China. 

Last year, The Mail on Sunday revealed that planning documents for the embassy included ‘spy dungeons’ – two suites of basement rooms and a tunnel, with their purpose redacted for security reasons.

Diplomatic sources also revealed that a proposed ‘spy campus’ will provide on-site accommodation for more than 200 intelligence officers at the embassy. 

A row has rumbled on about the planned mega embassy since 2018 when China bought the 215,280 sq ft site for £255million from the Crown Estate.

Security fears were immediately raised over the land’s proximity to sensitive underground communications in the Square Mile.

The cables along Mansell Street, which belong to companies including BT, Colt Technologies and Verizon, carry communications to and from financial institutions in the City of London.

They sit directly between financial hubs in the City and Canary Wharf and close to three major data centres, including the Stock Exchange. 

Those who have fled Hong Kong’s Chinese regime also fear the huge embassy would be used as a base to hunt them down. 

Copies of plans with redacted basement rooms revealed in The Mail on Sunday also heightened fears about China’s plans for the complex.

It revealed that planning documents for the controversial embassy include ‘two suites of anonymous unlabelled basement rooms and a tunnel’, with their exact purpose ‘redacted for security reasons’.

China has dismissed claims the embassy could be an espionage hub, while BT told the Telegraph it had ‘robust security measures in place’ and worked with the Government to protect its assets.

Shadow justice secretary Robert Jenrick said in a post on X that the unredacted plans were ‘shocking’, adding: ‘No one committed to our national security could possibly sign this off. But Kowtow-Keir will.’

A decision on whether to approve the embassy had been due on December 10, but was delayed to give Housing Secretary Steve Reed, who has the final say on major planning cases, to examine the proposal further.

Downing Street suggested that the consideration of ‘particular security implications’ meant that more time was needed to consider the planning application. 

Beijing later hit out at the decision, saying it was ‘completely unjustified’ and the reasons behind it were ‘untenable’.

It came amid suggestions that a failure to approve the new embassy in London could ruin Sir Keir’s plans to make his first official visit to China – expected to be between 29 to 31 January. 

The Ministry of Housing, Communities and Local Government said it was unable to provide a comment while the application is being assessed. The Daily Mail has contacted the Chinese Embassy in the UK for comment.