Chinese state security will be allowed to check people’s passports before they visit an ancient British heritage site in the heart of the City of London, The Mail on Sunday can reveal.

Chinese guards will carry out airport-style security checks on tourists who want to see the ruins of a Cistercian Abbey, St Mary Graces, endowed to the city by King Edward III in 1350.

The ring-of-steel has been approved by Foreign and Home Office officials because the ruins sit within the site of Beijing‘s proposed ‘super-embassy’.

The plan to build the embassy has been mired in controversy over claims that Sir Keir Starmer struck a secret deal with Beijing to approve the project – despite strong objections from Britain’s intelligence services.

Luke de Pulford, the executive director of the Inter-Parliamentary Alliance on China, said: ‘Legally speaking, Edward III’s foundation would be in China, and unsafe for anyone critical of the Chinese regime to visit.’

Former Tory leader Iain Duncan Smith said: ‘This is yet another example of the Labour Government caving into China’s bribery, blackmail, and bullying.

‘It is a grotesque compromise, which exposes the supine and pathetic attitude this once proud country has adopted towards China.’ 

A decision on the embassy will be made on December 10.

The development, on the site of a former Barclays trading floor, would have accommodation for more than 200 diplomats and intelligence officers, making it the largest embassy in Europe. 

A nearby tunnel has carried fibre optic cables under the Thames since 1985. 

The Bank of England has also highlighted the risks of allowing the embassy to be built close to sensitive financial centres.

The planning process was revived by Beijing after Sir Keir won last year’s General Election, with President Xi Jinping mentioning it directly to Chancellor Rachel Reeves when she visited China in January to discuss trade deals.

Critics have accused Ms Reeves of sacrificing national security in her desperation to fill a £30billion black hole in the public finances.