Investors wiped a fifth off Toshiba’s market value yesterday as they reassessed the company’s financial stability after its multibillion-dollar writedown warning.

Fund managers in Tokyo and Hong Kong said the nuclear-to-electronics conglomerate — once among the proudest names in corporate Japan — was fighting for survival with its slack corporate governance and repeated disclosure failures having “probably permanently” lost it the trust of investors.

As the shares sank 20 per cent under a glut of sell orders — and Japanese agency R&I downgraded Toshiba’s credit rating from BBB minus to BB — Tokyo traders said the market was trying to price in the possibility that Toshiba’s shareholder equity would be zero by the end of the current fiscal year in March. Bankers said efforts to shore up the company could involve a debt-for-