LONDON (Reuters)—The credit ratings of European insurers would be cut if Greece was to suffer a disorderly exit from the euro, causing a slump in the value of their investments, credit rating agency Fitch Ratings Inc. said on Wednesday.

Worst-hit would be insurers such as Assicurazioni Generali S.p.A. and Mapfre S.A. in fiscally-stretched Italy and Spain, seen as vulnerable because of their large holdings of their own countries' distressed sovereign and bank debt.

"In the case of a Greek exit, Italy would most likely be put on negative rating watch, and if Italy is downgraded, Generali would be one of the first Italian companies in line to be downgraded," said Fitch insurance analyst David Prowse.

If Greece's departure were managed so as to contain the market effects, insurers based in the economically healthier northern eurozone countries would likely survive with their credit ratings intact, Fitch said.

The industry would also be able to cushion the impact of a Greek exit by passing on some losses to customers who hold unit-linked products, where investment risk is shared by policyholders and shareholders.

Regulators probably would also relax solvency rules so as to help insurers cope with sharp falls in the value of their investment assets, Fitch said.

Some British life insurers would have been "on the brink of insolvency" during the 2008 financial crisis without such regulatory lenience, Fitch's Mr. Prowse said.

Italy's watchdog, the Instituto per la Vigilanza sulle Assicurazioni Private e di Interesse Collettivo, last year said insurers did not have to count all losses on sovereign debt when calculating their solvency ratios, shielding Generali, holder of 46 billion euros ($58.14 billion) of Italian gilts, from the full impact of the euro zone debt crisis.

Greek political parties that broadly support the terms of an international bailout deal for Greece narrowly won a general election on June 17, averting the immediate threat of the critically-indebted nation being forced out of the euro zone.

Fitch's operating assumption is that the single currency weathers the crisis without Greece leaving, although a departure cannot be ruled out, the rating agency said.