Support for the UK remaining in the European Union has dipped among business leaders, according to a British Chambers of Commerce (BCC) survey.
The BCC said that its final poll ahead of the 23 June vote suggested 54.1% were backing the Remain camp.
While that is a majority, it represented a fall from a figure of 60% back in February.
The BCC said 37% of the 2,200 bosses questioned were now supporting an exit – up from 30% – and 90% of the total said they were unlikely to change their minds before the referendum.
It added that big business was “significantly more likely” to support remaining in the bloc – as were companies which traded in the EU.
The business lobby group, unlike the CBI, has refused to take sides in the debate.
At the start of the campaign in March the BCC suspended its then-director general, John Longworth, who later quit after outlining his personal views in support of Brexit.
Dr Adam Marshall, who took over as acting director general following his departure, said of the poll’s results: “As the EU referendum campaign enters the final straight, the race for the business vote has clearly tightened.
“While only a minority of businesspeople report that the referendum campaign has had a material impact on their firms to date, much larger numbers say they expect significant impacts in the aftermath of the vote.”
The vote – and uncertainty surrounding the outcome – has been blamed in some quarters for contributing to a slowdown in the UK economy while the business debate has exposed deep divisions.
The Brexit camp has wheeled out a panel of economists alongside business leaders including former HSBC boss Michael Geoghegan and CMC Markets founder Peter Cruddas to warn that Brussels poses a threat to Britain’s financial services industry.
Sky News reported on Monday how JD Wetherspoon chairman Tim Martin was making a £200,000 donation to Vote Leave.
High profile supporters of the status quo include WPP founder Sir Martin Sorrell and BT chairman Sir Mike Rake – supporting the BCC’s finding that big business largely favours Remain.
The pro-EU side is believed to have raised significantly more in fighting funds for the campaign than its rivals, with Sky News reporting last week that donations to Britain Stronger In Europe had topped £14m.
Airbus is among the companies to have contributed.
City Editor Mark Kleinman said he expected Electoral Commission figures to show the £14m sum was more than double that achieved to date by Vote Leave.
Dr Marshall added: “Whichever outcome prevails, Westminster must shift its attention back to the economy on 24 June without delay.
“Growth is softening, and Westminster’s referendum ‘tunnel vision’ over the past year has meant that far too many key economic issues have been given short shrift or delayed altogether.”