A business leader is set to urge companies to "speak out early" in favour of remaining in a reformed European Union.
CBI president Sir Mike Rake will argue that the time is "ripe" for reforming the EU as the Government presses ahead with its promised in-out referendum.
He will tell the business group's annual dinner in London tonight that the time has come for business to "turn up the volume" on the issue in a language that people can understand.
"In the months to come, our country will have to make its own choice," he will say. "A choice between openness and isolation. Between shaping the future or retreating into the past.
"The question is not whether the UK would survive outside the EU, but whether it would thrive. No one has yet set out a credible alternative future.
"The current alternatives are not realistic options - little or no influence and the obligation to comply with EU principles whilst still paying most of the costs.
"Reform will not happen overnight, but by working with our allies on an ambitious, yet achievable, agenda, we can make it a reality. So we support the Prime Minister's drive for a more competitive EU, and the new Government can count on businesses' support to make this happen.
"Already, we are seeing a growing consensus,from Government, business and Europe's leaders. We have seen some encouraging signs of progress from the European Commission."
Sir Mike, chairman of BT, will also tell the 1,000 businesspeople set to attend the event that the regulatory environment in the UK is going "above and beyond" other countries, leading to "unmistakable signs" of activity being diverted.
"We need to retain major global institutions based in London - key to our reputation as a global hub and to our world-beating legal, accounting and other professional services," he will add.
Sir Mike will further call for efforts to tackle the UK's poor productivity by investing in skills and education. And he will claim that devolution can be "part of the solution".