One official said some 30 mainly ex-fast jet but also some helicopter pilots - lured by annual salaries of around £240,000 - are currently in
China training pilots for the People's Liberation Army, in what a defence analyst described as a stunning breach of security.
The situation is so grave, the Ministry of Defence's Defence Intelligence service on Tuesday issued a "threat alert" to warn serving and former military personnel against such approaches.
China is using third-party head-hunters, including a company based in South Africa, to target personnel, the western official said.
The official named the company as the Test Flying Academy of South Africa, though stressed it had no connection with the South African government.