HIH, an Australian insurer which owns Lloyd's syndicate HIH Cotesworth has had its shares suspended on the Australian stock exchange twice in the same week after plunging an estimated Aus$500m (£176m) into the red.
Director Rodney Stephen Adler has resigned following the news.
And the Australian Securities & Investments Commission is investigating whether the company kept the market adequately informed of its trading positions.
HIH owns all the shares of Lloyd's syndicate HIH Cotesworth. It also formed a partnership with the Gerling Group last year, and now HIH writes industrial business through Gerling Australia Insurance.
It is thought losses could total up to Aus$500m (£176m) and HIH has in the past said it overpaid Aus$200m (£80m) when acquiring FAI in 1998.