The BCC asked 2,000 senior business leaders what they would do if the vote were held tomorrow, and found 63 per cent said they would vote to remain in the EU, while 27 per cent said they would vote for a Brexit.
Ten per cent said they were unsure. Yet half of those surveyed said they could change their mind depending on the reforms Cameron is or is not able to secure, with BCC director general John Longworth having said: "Many assume that the EU referendum is a simple in-out debate where both camps are firmly entrenched in their positions, but this survey shows that business people want more information and greater clarity, and for now at least their vote is still up for grabs."
Some 40 per cent of businesses surveyed thought leaving the EU would have negative consequences for their businesses, while 40 per cent think it would make no difference. Just 14 per cent thought it would have a positive impact.
Cameron has promised a vote by the end of 2017, after he pursues a reform package with the EU.
The announcement from the BCC comes on the same day the UK Independence Party kicks off it's annual conference, with leader Nigel Farage expected to say his priority is leaving the European Union, and not his party.