The majority of business people plan to vote for the UK to remain in the EU but the gap with those wanting to leave has narrowed, a survey suggests.
The British Chambers of Commerce (BCC) said 54% of 2,200 members it surveyed in April said they would vote Remain, down from 60% in February's survey.
In contrast, 37% said they would vote to leave, up from 30% two months ago.
Almost all of those surveyed - 90% - said they were unlikely to change their opinion ahead of the 23 June vote.
The BCC's acting director general Dr Adam Marshall said the gap had "clearly tightened".
"Although a clear majority of the business people we surveyed continue to express a preference to remain in the European Union, the gap between Remain and Leave has narrowed significantly in recent weeks," he added.
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The BCC is a national body of 52 accredited chambers of commerce across the UK, representing thousands of large, medium and small businesses.
Larger firms and those trading with other EU markets were more likely to vote to remain in the EU, while those in "micro" firms with under 10 staff and those which did not export were more likely to vote to leave the EU, the BCC's survey found.
The majority of business leaders surveyed said the referendum had had no impact so far on various aspects of their businesses, including sales, recruitment and investment.
If the UK was to leave the EU, 35.9% said they expected this to have a negative impact on their overall growth strategy, while 36.3% felt it would have no impact and 15.9% said it would have a positive impact.
'Leap in the dark'
Britain Stronger in Europe, the official Remain campaign group, said the survey made it clear the majority of businesses wanted Britain to stay in the EU.
"Membership of the EU has made our economy more open and competitive, with British businesses able to access 500 million consumers through the single market.
"Walking away would be a leap in the dark. So it's unsurprising that today's poll confirms that British business is adamant that we must stay in the EU," said Britain Stronger in Europe executive director Will Straw.
John Longworth, the chairman of the Vote Leave campaign's business council and the former director general of the BCC, said the survey showed businesses were rejecting the Remain campaign's "main tactic of talking down Britain and its dynamic economy".
"Despite the claims of the pro-EU camp to the contrary, business is not fearful of the referendum or the result. This is because they know it is safer to take back control and spend our money on our priorities," he said.
Mr Longworth resigned from the BCC in March after being suspended for saying the UK's long-term prospects could be "brighter" outside the EU.
The BCC has said it will not campaign for either side in the 23 June referendum as its membership is split.
Adding to the debate on the impact of Brexit on the UK's economic prospects, the research body the National Institute of Economic and Social Research (NIESR) predicts that sterling could slide by 20% in the immediate aftermath of a UK vote to leave.
The body added that it would be likely to result in the economy growing by 1.9% in 2017, compared with a rate of 2.7% if the UK votes to remain.
"Heightened risk and uncertainty will cause sterling to depreciate by around 20% immediately following the referendum, which will result in an intense bout of inflationary pressure," NIESR said.
Those forecasts came as a group of economists campaigning to leave argued that a recent Treasury analysis suggesting that Brexit would lead to an 8% fall in GDP was fundamentally flawed.
Economists for Brexit said it used "methods that have no foundation in economic theory".
"Brexit is a major reform that is disruptive of existing market relationships," said Prof Patrick Minford, from Economists for Brexit, and therefore a "proper underlying, structural model" was needed.
He argued that the method used by the Treasury failed to take into consideration major changes in tariffs, trade barriers and an overhaul in regulations.
His analysis suggests the economy would in fact grow by 4%.