Labour wants British businesses to wade into the debate over the UK’s future in Europe, saying they risk being too late to stem the rising sceptic tide in the country.

The shadow foreign secretary, Douglas Alexander, appeals to wavering chief executives to recognise they have a patriotic duty as well as a commercial self-interest to find their voice now. He wants them to make the case with authority and passion, rather than to prevaricate until the last days of a possible referendum campaign. Insisting the issue of Europe transcends politics, he will say on Monday: “Your voice must be heard because if you wait, it could be too late. That risk is real.”

Alexander’s remarks reflect a growing fear that some business executives are going to try to sit out the referendum campaign or as in the Scottish referendum campaign only intervene close to polling day.

In a speech to European diplomats, Alexander will argue: “The starting gun on the campaign to keep Britain in Europe has been fired. And Britain needs you to join in the race. The work begins now. Now is the time to speak out. Now is the time to speak up”.

Alexander is also meeting senior executives for a Labour business summit, and with Labour leader Ed Miliband last week held private talks with 10 senior company chief executives to discuss Europe.

He points to recent polling by YouGov of more than 700 business leaders across the UK showing an increase in those who believe the prospect of Britain leaving the European Union had gone up in the last six months. The poll showed nearly 80% thought the prospect of Britain leaving Europe had gone up and amongst business leaders in the manufacturing sector, it was closer to 90%. A quarter of all the businesses leaders contacted thought it had gone up significantly.

Alexander says: “These figures show the mounting concern within the business community. But mounting concern has not yet been matched by increased engagement through the public debate”. Drawing on his experience in Scotland, where Alexander threw himself into the No Campaign, he says: “ I know, from private and public discussions, that many businesses in Scotland had been aware of the risks of separation for a long time. And I do understand why they were reluctant to speak out. They didn’t want to become political targets. But today I want to make the case that we should learn from our experience of that referendum in Scotland.

“Once again business faces the dilemma of how to face down a populist leader mobilising and an increasingly angry public campaign. Last summer it was about Scotland leaving the UK. Next summer it could be about the UK leaving Europe.

“I know that some companies may feel that now is not the time to speak up on our membership of the EU. Perhaps they think that this is something that can and should wait until the moment of decision. That was the revealed preference of some businesses in Scotland over the summer. For business to speak up for Britain’s place in Europe is not about party political advantage, it is about recognising where our country’s national interest and your business interests lies. It is about patriotic duty and good business sense.”

He insists that Labour would make the case for reform, pointing to plans for countries outside the eurozone to have permanent observer status at Eurogroup meetings and at a new council on the single market.

Alexander believes the issue of Europe may be a bridgehead for Labour to build a stronger relationship with business so at least the voice of business will not be uniformly unwilling to support Labour as was the case in 2010 election.

In his speech, Alexander will say: “Leaving the EU means permanently ending one of our nation’s long-running economic successes. It means actively choosing an economy with weaker investment, less trade with the rest of the world, poorer productivity and worse living standards.”