Allen Ho was still reeling from his arrest during a conference in Atlanta, Georgia, when armed Federal Bureau of Investigation agents began interrogating the nuclear energy consultant about his work in China, without any lawyer present.

That business involved hiring retired US nuclear engineers and consultants to advise China General Nuclear Power Corp, the state-owned company that plans to invest in an ￡18bn reactor in the UK.

Mr Ho, born in Taiwan and a US citizen since 1983, was charged with violating a statute designed to prevent American scientists from helping other countries develop an atomic bomb. The case comes during an era of unprecedented nuclear co-operation between the west and China, but also a time of growing trade friction and accusations of cyber crime and espionage.