BHP was among the companies helped by Australian spy agencies as they negotiated trade deals with Japan, a former Australian Secret Intelligence Service officer says.

A former diplomat has also confirmed Australian intelligence agencies have long targeted Japanese companies. Writing in The Japan Times, Professor Gregory Clark said Australian companies were beneficiaries of intelligence operations.

"In Australia, favoured firms getting spy material on Japanese contract policies and other business negotiations used to joke how [it had] 'fallen off the back of a truck'," Professor Clark wrote.

Business information is a main target for [intelligence] agencies, he said. "The targeting is also highly corrupting since the information can be passed on selectively to co-operative firms - often firms that provide employment and cover for spy operatives."