A top aide to Gordon Brown has been a suspected victim of a “honeytrap” operation by Chinese intelligence agents.

The aide, a senior Downing Street adviser who was with the prime minister on a trip to China earlier this year, had his BlackBerry phone stolen after being picked up by a Chinese woman who had approached him in a Shanghai hotel disco.

The aide agreed to return to his hotel with the woman. He reported the BlackBerry missing the next morning.

The aide, whose identity is known to The Sunday Times, immediately reported the theft to the prime minister’s Special Branch protection team and was informally reprimanded.

A senior official said yesterday that the incident had all the hallmarks of a suspected honeytrap by Chinese intelligence. The incident will raise fresh questions about the security of sensitive official information. It follows a spate of high-profile cases where data from government departments have been lost.

BlackBerrys are used as mobile telephones and also store data and send and receive e-mails. Downing Street BlackBerrys are password-protected but security officials said most are not encrypted.

Experts say that even if the aide’s device did not contain anything top secret, it might enable a hostile intelligence service to hack into the Downing Street server, potentially gaining access to No 10’s e-mail traffic and text messages.

The incident highlights the growing threat of Chinese intelligence to Britain and the West. Last December Jonathan Evans, the director-general of MI5, warned that China was carrying out state-sponsored espionage against vital parts of Britain’s economy, including the computer systems of big banks and financial services firms.

Sources said that the incident had occurred during Brown’s two-day trip to China in January.

The prime minister had been accompanied by about 20 Downing Street staff, including senior advisers on foreign policy, the environment and trade. There were also 25 business leaders on the trip, among them Sir Adrian Montague, the chairman of British Energy, Arun Sarin, then chief executive of Vodafone, and Sir Richard Branson, the Virgin boss.

The incident occurred in Shanghai on the second day of the tour. That evening, about a dozen members of the Downing Street staff went to a hotel disco where a lively party with several hundred young people was in full swing.

“It was apparently a lot of fun, there was quite a bit of dancing with lots of people ona big crowded dance floor,” said one security official.

The group stayed at the disco for at least two hours. One senior aide was approached by an attractive Chinese woman. The couple danced and later disappeared together.

The security official said: “In these circumstances it was not wise. Nobody knows exactly what happened after they left. But the next morning he came forward and said: “My BlackBerry is missing.” The prime minister’s Special Branch protection team were alerted.

Downing Street yesterday confirmed that a member of the prime minister’s office had lost a BlackBerry during an evening event on the January visit to China. However, it played down the affair, stating that an investigation had established that there was “no compromise to security”.

Last week it emerged that US intelligence and security officials were debating whether to warn business people and other travellers heading to the Beijing Olympics about the dangers posed by Chinese computer hackers.

Joel Brenner, the US government’s top counter-intelligence official, warned: “So many people are going to the Olympics and are going to get electronically undressed.”