A proposed $420m (€343m) rights issue from Converium, the Swiss reinsurer, could be at risk after its latest ratings downgrade breached the underwriting conditions for the equity offer. Credit Suisse First Boston and JP Morgan are leading the proposed deal.

Standard & Poor's, the international credit ratings agency, lowered its long-term rating on Converium from A- to BBB after the market close on Friday. S&P cited management's loss of credibility and concerns over Converium's ability to retain and attract business.