Mr Nishi, operating through his company Winchester Metals (Tokyo), is said to have been involved with Mr Hamanaka in a series of copper trading activities.
It remains unclear whether Winchester Metals is the same company as the one sold for pounds 65,000 by the UK copper trading firm Winchester Commodities in June 1993. Winchester Commodities had previously been investigated, and cleared, by the Securities and Futures Authority for its own activities linked to copper trading.
A Winchester Commodities spokesman said the identity of the purchaser of 90 per cent of the interest in its Tokyo subsidiary had never been revealed. One Winchester Metals employee, who would not be named, confirmed yesterday that Mr Nishi had owned "most" of the business for several years.
Operating through Winchester Metals, Mr Nishi was named by David Threlkeld, the metal dealer and whistleblower, as the person to whom he was asked to confirm non-existent trades with Sumitomo in October 1991.
Mr Threlkeld sold his own Tokyo business to Mr Nishi for $80,000 (pounds 50,000) in June 1992.
Mr Nishi, said by Mr Threlkeld to be a former Merrill Lynch employee, is likely to face questioning by financial investigators over his dealings with Mr Hamanaka.