A vote in favour of independence could trigger negative rating action against insurance companies operating in Scotland, Standard & Poor's warned today.
Uncertainties such as what currency Scotland will use if it votes on September 18 to leave the UK or whether it will be a member of the European Union could affect ratings.
Scottish tax and regulatory rules might diverge from those of the UK, adding complexities and raising costs for insurers, the ratings agency said.
"Insurers with discrete Scottish subsidiaries would feel the greatest rating impact from a "yes" vote," S&P said.
Recent opinion polls have suggested Scottish separatists are closing the gap on their unionist rivals before the September referendum, though a rejection of independence still looks likely.
"Even if the `No' campaign is victorious, both major UK parties have promised to devolve further powers to the Scottish parliament - a shift that could itself impact the insurance sector," the agency cautioned.
Meanwhile, over 100 business leaders in the UK with operations in Scotland plan to speak out against independence in a united statement, the Telegraph newspaper has reported.
The newspaper said Keith Cochrane, chief executive of Glasgow-based engineer Weir Group, was behind the move urging business leaders and entrepreneurs to sign a joint letter imploring voters to reject independence for the sake of economic prosperity.
Those approached included Royal Mail Chairman Donald Brydon, Cairn Energy boss Bill Gammell, Aggreko interim CEO Angus Cockburn and Royal Dutch Shell chief executive Ben van Beurden, the Telegraph said.
The newspaper said the full list would be disclosed next week.
So far, most companies have refrained from making public comments as their workforces are divided on the issue of independence for Scotland.
The newspaper said signatories have put their names to the list in a personal capacity.