The poll by executive search firm Korn Ferry found 65 percent of chairmen of 32 FTSE 100 companies said it would be bad for business if Scotland ended its 307-year union with England while 24 percent saw it as good or very good.

Commenting on a "Yes" vote for independence, one chairman said it would be "particularly bad for the Scots, not good for the English and would dilute the UK's economic influence".

The survey was released as an increasing number of business leaders take sides or point out risks ahead of the independence vote on September 18.

Debate has lately focused on whether an independent Scotland could keep the pound and stay in the EU.

Latest opinion polls show separatists still trailing in public support but gaining ground, with UK government officials warning against complacency.

The first major business leader publicly to oppose Scottish independence was Bob Dudley, head of Britain's second-biggest oil company BP (>> BP plc) who warned over the uncertainties that could come with Scottish independence.

But Scotland's First Minister Alex Salmond pointed out on Monday that BP was continuing to invest in the North Sea.

RBS (>> Royal Bank of Scotland Group plc), Bank of Scotland-owner Lloyds Banking Group (>> Lloyds Banking Group PLC) and other major financial institutions based in Edinburgh have begun contingency planning in the event of a vote for independence, as reported by Reuters.

A previous survey by Korn Ferry and the British Retail Consortium found 33 retail chairmen were "consistently negative" about Scottish independence, concerned about possible impact of new employment and pension laws and rising supply chain costs.

Outgoing chief executive of supermarket Sainsbury, Justin King, has warned independence could lead to higher food prices.

The Korn Ferry poll, taken from its latest Boardroom Pulse survey, also found an overwhelming majority of chairmen, 98 percent, did not think a EU referendum would result in the UK leaving the bloc, up from 81 percent in a survey last March.

It found the number of chairmen who saw leaving the EU as bad for business had risen to 86 percent from 74 percent.

"The chairmen of our largest companies have spoken out in favour of keeping the Union and staying in the EU. They believe this is in the best interests of British business and the wider economy," said Korn Ferry spokesman Dominic Schofield.

(Reporting by Belinda Goldsmith; editing by Stephen Addison)