The Chinese official was intercepted by members of the British diplomatic protection squad when he posed as an official interpreter, The Sunday Times reported citing documents circulating in Whitehall, the centre of the British government.
British officials believe the Chinese agent wanted to join Xi and the Queen in her royal carriage. When the ruse was rumbled it led to heated exchanges, the daily said citing three senior figures who confirmed details of the incident.
A royal source said, "No one got into the carriage except the principals." But details of the spat came amid concern that the security services were too quick to do China's bidding during the state visit.
"There was a stand-off and our protection people were shouldered aside. There's an issue here about bullying, uncomprehending Chinese police. This security should be done by us, not them," a senior Tory said.
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Chinese officers are now likely to train at Sandhurst and Dartmouth, the army and naval training colleges.
The move risks antagonising allies in America and Japan, who are locked in a dispute with China in the South China Sea.
President Xi was on a state visit to the UK from October 20-23.